Coverage Policy Manual
Policy #: 2002002
Category: Laboratory
Initiated: January 2002
Last Review: April 2022
  Genetic Test: Azothiaprine, 6MP Sensitivity,Genotyping & Phenotyping (TPMT) (NUDT15)

Description:
Thiopurines or purine analogues are immunomodulators. They include azathioprine (Imuran), mercaptopurine (6-MP; Purinethol), and thioguanine (6-TG; Tabloid). Thiopurines are used to treat malignancies, rheumatic diseases, dermatologic conditions, and inflammatory bowel disease, and are used in solid organ transplantation. They are considered an effective immunosuppressive treatment of inflammatory bowel disease, particularly in patients with the corticosteroid-resistant disease. However, the use of thiopurines is limited by both long onset of action (3-4 months) and drug toxicities, which include hepatotoxicity, bone marrow suppression, pancreatitis, and allergic reactions.
 
Thiopurines are metabolized by a complex pathway to several metabolites including 6-thioguanine (6-TG) and 6-methylmercaptopurine (6-MMP). Thiopurine methyltransferase (TPMT) is one of the key enzymes in thiopurine metabolism. Patients with low or absent TPMT enzyme activity can develop bone marrow toxicity with thiopurine therapy due to excess production of 6-TG metabolites, while elevated 6-MMP levels have been associated with hepatotoxicity (Vande Casteele, 2017). In population studies, the activity of the TPMT enzyme has been shown to be trimodal, with 90% of subjects having high activity, 10% intermediate activity, and 0.3% with low or no activity. Variants in another metabolizing enzyme, NUDT15 (nudix hydrolase, NUDIX 15), have been identified that strongly influence thiopurine tolerance in patients with IBD (Yang, 2014). Homozygous carriers of NUDT15 variants are intolerant of thiopurine compounds because of risk of bone marrow suppression. Individuals with this variant are sensitive to 6-MP and have tolerated only 8 percent of the standard dose. Several variant alleles have been identified with varying prevalence among different populations and varying degrees of functional effects (Moriyama, 2017). NUDT deficiency is most common among East Asians (22.6%), followed by South Asians (13.6%), and Native American populations (12.5%-21.2%). Studies in other populations are ongoing (Mayo Clinic Laboratories, 2020).  
 
Clinical laboratories may develop and validate tests in-house and market them as a laboratory service; laboratory-developed tests must meet the general regulatory standards of the Clinical Laboratory Improvement Amendments. Several thiopurine genotypes, phenotype, and metabolite tests are available under the auspices of the Clinical Laboratory Improvement Amendments. Laboratories that offer laboratory-developed tests must be licensed by the Clinical Laboratory Improvement Amendments for high-complexity testing. To date, the U.S. Food and Drug Administration has chosen not to require any regulatory review of this test.
 
Prometheus is a commercial laboratory that offers thiopurine genotype, phenotype and metabolite testing for those undergoing thiopurine therapy. The tests are referred to as Prometheus TPMT Genetics, Prometheus TMPT enzyme, and Prometheus thiopurine metabolites, respectively. Other laboratories that offer TPMT genotyping include Quest Diagnostics (TPMT Genotype), ARUP Laboratories (TPMT, DNA); Specialty Laboratories (TPMT GenoTypR™), PreventionGenetics (TPMT Deficiency via the TPMT Gene); Genelex (TPMT); Fulgent Genetics (TPMT); and LabCorp (TPMT enzyme activity and genotyping).
 
The FDA has included pharmacogenomics information in the physician prescribing information (drug labels) of multiple drugs. In most cases, this information is general and lacks specific directives for clinical decision making. In the following examples, the FDA has given clear and specific directives on use of pharmacogenomic testing for azathioprine (a prodrug for mercaptopurine), mercaptopurine, and thioguanine.
 
Mercaptopurine (Purixan, 2020)
    • Consider testing for TPMT and NUDT15 deficiency in patients who experience severe myelosuppression or repeated episodes of myelosuppression Homozygous Deficiency in either TPMT or NUDT15: Patients with homozygous deficiency of either enzyme typically require 10% or less of the recommended dosage. Reduce the recommended starting dosage in patients who are known to have homozygous TPMT or NUDT15 deficiency.
    • Heterozygous Deficiency in TPMT and/or NUDT15: Reduce the dosage based on tolerability. Most patients with heterozygous TPMT or NUDT15 deficiency tolerate recommended dosage, but some require dose reduction based on adverse reactions. Patients who are heterozygous for both TPMT and NUDT15 may require more substantial dose reductions.
 
Azathioprine (Imuran, 2020)
    • Patients with TPMT and/or NUDT15 Deficiency: Consider testing for TPMT and NUDT15 deficiency in patients who experience severe bone marrow toxicities. Early drug discontinuation may be considered in patients with abnormal CBC results that do not respond to dose reduction
    • Homozygous deficiency in either TPMT or NUDT15: Because of the risk of increased toxicity, consider alternative therapies for patients who are known to have TPMT or NUDT15 deficiency
    • Heterozygous deficiency in TPMT and/or NUDT15: Because of the risk of increased toxicity, dosage reduction is recommended in patients known to have heterozygous deficiency of TPMT or NUDT15. Patients who are heterozygous for both TPMT and NUDT15 deficiency may require more substantial dosage reductions.
 
Thioguanine (Tabloid, 2020)
    • Consider testing for TPMT and NUDT15 deficiency in patients who experience severe bone marrow toxicities or repeated episodes of myelosuppression.
    • Evaluate patients with repeated severe myelosuppression for TPMT or NUDT15 deficiency. TPMT genotyping or phenotyping (red blood cell TPMT activity) and NUDT15 genotyping can identify patients who have reduced activity of these enzymes. Patients with homozygous TPMT or NUDT15 deficiency require substantial dosage reductions.
 
Coding
 
Effective January 2018, there is a specific Proprietary Laboratory Analysis (PLA) code for gene analysis of TPMT and NUDT15. CPT 0034U is specifically for use with the Thiopurine Methyltransferase (TPMT) and Nudix Hydrolase (NUDT15) Genotyping test performed by Mayo Clinic laboratory.
 
0034U TPMT (thiopurine S-methyltransferase), NUDT15 (nudix hydroxylase 15) (eg, thiopurine metabolism), gene analysis, common variants (ie, TPMT*2, *3A, *3B, *3C, *4, *5, *6, *8, *12; NUDT15*3, *4, *5)
 
Effective in 2012, the analysis of common variants of the TPMT gene would be reported with CPT code 81401
 
81401 Molecular pathology procedure, Level 2 (e.g., 2-10 single nucleotide polymorphisms [SNPs], 1 methylated variant, or 1 somatic variant [typically using nonsequencing target variant analysis], or detection of a dynamic mutation disorder/triplet repeat).
 
Effective January 2022, there is a specific Proprietary Laboratory Analysis (PLA) code for gene analysis, common variants of CEP72, NUDT15 and TPMT (CNT genotyping panel). CPT 0286U is specifically for use with the genotyping panel performed by RPRD Diagnostics.
 
0286U CEP72 (centrosomal protein, 72-KDa), NUDT15 (nudix hydrolase 15) and TPMT (thiopurine S-methyltransferase) (eg, drug metabolism) gene analysis, common variants
 
There are no specific CPT codes for metabolite markers of azathioprine, mercaptopurine (6-MP) or thioguanine.  
   
For coverage of metabolite markers please see policy # 2009022.

Policy/
Coverage:
Effective January 2022
 
Meets Primary Coverage Criteria Or Is Covered For Contracts Without Primary Coverage Criteria
 
One-time genotypic or phenotypic analysis of the TPMT or NUDT 15 meets member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes for patients beginning therapy with azathioprine (AZA), mercaptopurine (6-MP) or thioguanine (6-TG) OR for  patients on thiopurine therapy with abnormal complete blood count (CBC) results that do not respond to dose reduction and in pediatric patients with acute lymphoblastic leukemia who are to be treated with thiopurine chemotherapy.
 
Does Not Meet Primary Coverage Criteria Or Is Investigational For Contracts Without Primary Coverage Criteria
 
Genotypic or phenotypic analysis of TPMT or NUDT15  for any indication not listed above does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, genotypic or phenotypic analysis of TPMT or NUDT15  for any indication other than listed is considered investigational. Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
Gene analysis of CEP72, NUDT15 and TPMT (common variants) does not meet member benefit certificate primary coverage criteria that there be scientific evidence of effectiveness in improving health outcomes.
 
For members with contracts without primary coverage criteria, gene analysis of CEP72, NUDT15 and TPMT (common variants) is considered investigational. Investigational services are specific contract exclusions in most member benefit certificates of coverage.
 
Effective April 2018 to December 2021
 
One-time genotypic or phenotypic analysis of the TPMT or NUDT 15 meets primary coverage criteria for patients beginning therapy with azathioprine (AZA), mercaptopurine (6-MP) or thioguanine (6-TG) OR for  patients on thiopurine therapy with abnormal complete blood count (CBC) results that do not respond to dose reduction and in pediatric patients with acute lymphoblastic leukemia who are to be treated with thiopurine chemotherapy.
 
Genotypic or phenotypic analysis of TPMT or NUDT15  for any indication not listed above does not meet primary coverage criteria for effectiveness.
 
For contracts without primary coverage criteria genotypic or phenotypic analysis of TPMT or NUDT15  for any indication other than listed above is considered investigational.  Investigational services are an exclusion in the member benefit certificate.
 
Effective August 2009 – March 2018
One-time genotypic or phenotypic analysis of the TPMT meets primary coverage criteria for patients beginning therapy with azathioprine (AZA), mercaptopurine (6-MP) or thioguanine (6-TG) OR for  patients on thiopurine therapy with abnormal complete blood count (CBC) results that do not respond to dose reduction and in pediatric patients with acute lymphoblastic leukemia who are to be treated with thiopurine chemotherapy.
 
Genotypic or phenotypic analysis of TPMT for any indication not listed above does not meet primary coverage criteria for effectiveness.
 
For contracts without primary coverage criteria genotypic or phenotypic analysis of TPMT for any indication other than listed above is considered investigational.  Investigational services are an exclusion in the member benefit certificate.
 
Effective 2006
Analysis of the metabolite markers of azathioprine and 6-mercaptopurine, including 6-MMP and 6-TG is covered for members with inflammatory bowel disease who are unresponsive to azathioprine after six months of continuous therapy.  
  
Analysis of the metabolite markers of azathioprine and 6-mercaptopurine, including 6-MMP and 6-TG, is covered for members with collagen vascular disease who are unresponsive to azathioprine after six months of continuous therapy.
  
Measurement of TPMT genotype to identify homozygous TPMT deficient patients is covered for pediatric patients with acute lymphoblastic leukemia who are to be treated with thiopurine chemotherapy.
  
For group contracts furnished or renewed on or after July 1, 2004 or individual contracts furnished on or after July 1, 2004, genotypic analysis of the TPMT gene and the analysis of the metabolite markers in other circumstances do not meet Primary Coverage Criteria for effectiveness.
 
For those individual contracts in force prior to July 1, 2004, genotypic analysis of the TPMT gene and the analysis of the metabolite markers in other circumstances  are considered investigational.  Investigational services are an exclusion in the member certificate of coverage.
 
Effective 2003
Genotypic analysis of the TPMT gene is considered investigational and is not covered.
  
Analysis of the metabolite markers of azathioprine and 6-mercaptopurine, including 6-MMP and 6-TG is covered for members with inflammatory bowel disease who are unresponsive to azathioprine after six months of continuous therapy.  
  
Analysis of the metabolite markers of azathioprine and 6-mercaptopurine, including 6-MMP and 6-TG, is covered for members with collagen vascular disease who are unresponsive to azathioprine after six months of continuous therapy.
  
The analysis of the metabolite markers in other circumstances would be considered investigational and not covered.  Investigational services are a benefit contract exclusion.
 
Effective 2002
Genotypic analysis of the TPMT gene is considered investigational and is not covered.
  
Analysis of the metabolite markers of azathioprine and 6-mercaptopurine, including 6-MMP and 6-TG is covered for members with inflammatory bowel disease who are unresponsive to azathioprine after six    months of continuous therapy.  The analysis of the metabolite markers in other circumstances would
be considered investigational and not covered.  Investigational services are a benefit contract exclusion.

Rationale:
There are 3 steps in the technology assessment process: evaluation of technical performance, evaluation of ability to accurately diagnose a clinical condition compared with the criterion standard, and determination of whether use of the test results in an improved patient outcome. These factors are discussed next, both for pharmacogenomics and metabolite markers.
 
TECHNICAL PERFORMANCE
 
Pharmacogenomics
The genotypic analysis of the thiopurine methyltransferase (TPMT) gene is based on well-established polymerase chain reaction (PCR) technology to detect 3 distinct mutations. Currently, 3 alleles (TPMT*2, TPMT*3A, TPMT*3C) account for about 95% of subjects with reduced TPMT enzyme activity. Subjects homozygous for these alleles are TPMT-deficient and those heterozygous for these alleles have variable TPMT (low or intermediate) activity. A 2011 study from Sweden addressed the concordance between TPMT genotyping and phenotyping (Hindorf, 2012).  The investigators evaluated data from 7195 unselected and consecutive TPMT genotype and phenotype tests. The genotype tests examined the 3 most common TPMT variants, previously noted. TPMT genotyping identified 89% as TPMT wild type, 704 (10%) as TPMT heterozygous, and 37 (0.5%) as TPMT homozygous. The overall agreement between genotyping and phenotyping was 95%. Genotyping alone would have misclassified 3 (8%) of 37 homozygous patients as heterozygous; these 3 subjects were found to have uncommon mutations. All 3 had low TPMT activity. The phenotype test would have misclassified 4 (11%) of 37 of homozygous patients because they had test results above the cutoff level for low TPMT activity (<2.5 U/mL red blood cells [RBCs]).
 
Metabolite Markers
Metabolite markers have been assessed using high-performance liquid chromatography technology. It would be optimal to assess metabolite markers in peripheral leukocytes, because they reflect the status of bone marrow precursors. However, it is technically easier to measure metabolites in RBCs than in leukocytes.
 
Section Summary: Technical Performance
TPMT genotypic analysis via PCR technology is expected to have high performance. Concordance between genotypic and phenotypic analysis for TPMT activity is high in at least one analysis.
 
DIAGNOSTIC PERFORMANCE
 
Pharmacogenomics
Several systematic reviews of studies on the diagnostic performance of TPMT genotyping have been published. Among the most recent was a 2011 review by Booth et al sponsored by the Agency for Healthcare Research and Quality (Booth, 2011).  Nineteen studies on test performance were identified; most were cross-sectional or prospective observational studies and approximately 70% included patients with inflammatory bowel disease (IBD). Among the 1735 total patients, 184 were heterozygous and 16 were homozygous for variant alleles, a small subsample of subjects with variant alleles. Pooled analysis of data from 19 studies found a sensitivity of 79.9% (95% confidence interval [CI], 74.8% to 84.6%) for correctly identifying subjects with subnormal (intermediate or low) enzymatic activity. The specificity of the wild-type genotype for correctly identifying subjects with normal or high enzymatic activity approached 100%. Seventeen studies addressed the association between TPMT status and thiopurine toxicity. The studies included 2211 patients, 357 of whom had intermediate and 74 had low enzymatic activity. In a pooled  analysis of 3 studies (92 patients, 10 events), there were greater odds of myelotoxicity with low TPMT enzymatic activity than intermediate activity (pooled odds ratio [OR], 14.5; 95% CI, 2.78 to 76.0). Similarly, in a pooled analysis of 3 studies (403 patients, 29 events), there were greater odds of myelotoxicity with low TPMT enzymatic activity than with normal levels (pooled OR=19.1; 95% CI, 4.6 to 80.2). It is worth noting that the confidence intervals were wide due to few events and small sample sizes.
 
Another systematic review published in 2011, by Donnan et al, identified 17 studies that reported the performance characteristics of TPMT genotyping tests (12 studies) and phenotyping (6 studies) compared with a reference standard (Donnan, 2011). No true criterion standard was available. The enzymatic test was used as the reference standard in 9 studies, and the remainder used a genotyping test; 3 studies compared 2 methods of genotyping. All studies used a method of genotyping as either the investigational test or the reference standard; the tests varied somewhat in the number and type of polymorphisms they were designed to detect. Sixteen of 17 studies either reported sensitivity and specificity, or reported sufficient data for these measures to be calculated. Only 3 studies considered confounding factors (eg, concurrent medications, blood transfusions) in their exclusion criteria. Reviewers did not pool study findings. In the included studies, sensitivity of enzymatic tests ranged from 92% to 100% and the specificity ranged from 86% to 98%. The sensitivity of the genotype tests ranged from 55% to 100% and the specificity from 94% to 100%. In general, the enzymatic tests had a high sensitivity and a low positive predictive value (PPV) when genotype tests were used as the reference standard. Genotype tests showed a lower sensitivity and a high PPV when enzymatic tests were used as the criterion standard. The inconsistent use of a reference standard complicated interpretation of the findings.
 
A 2015 meta-analysis by Liu et al evaluated the relation between TPMT polymorphisms and adverse drug reactions (ADRs) in patients with IBD taking thiopurine drugs (Liu, 2015). This study updated a 2010 meta-analysis by Dong et al, and findings of the 2 analyses were similar (Dong, 2010). The Liu review included studies that compared TPMT polymorphism frequencies in patients who did and did not experience ADRs. The investigators initially screened 353 articles, and 14 studies (total N=2276 IBD patients) were ultimately found to meet eligibility criteria. In a meta-analysis of data from 10 studies, 67 of 476 patients with (14.1%) and 57 (4.8%) of 1192 patients without an ADR were TPMT heterozygous or homozygous. The pooled odds ratio was 3.36 (95% CI, 1.82 to 6.19), and the difference between groups was statistically significant. In analyses of specific adverse reactions, there were statistically significant associations between the presence of TPMT alleles and bone marrow toxicity, but not hepatotoxicity, pancreatitis, or other ADRs (eg, gastric intolerance, skin reactions). The number of events in some analyses was relatively small and these studies may have been underpowered to detect differences between groups. For example, 2 (3.3%) of 62 IBD patients with pancreatitis were TPMT heterozygous or homozygous compared with 116 (7.7%) of 1500 patients without pancreatitis (OR=0.97; 95% CI, 0.38 to 2.48).
 
In 2016, Roy et al reported on the association between TPMT genotype or phenotype tests and a reference standard, such that it was possible to determine sensitivity, specificity, PPV, negative predictive value, or concordance, in patients receiving thiopurines (Roy, 2016). Sixty-six studies were included and appraised for quality. Based on data from 25 studies reporting on test performance on genotyping, the calculated sensitivity for TPMT genotyping to detect a heterozygous or homozygous TPMT mutation ranged from 13.4% to 100.0%, while the specificity ranged from 90.9% to 100.0%. A smaller 2016 systematic review by Zur et al reported higher sensitivities and specificities for TPMT genotyping (Zur, 2016).
 
No systematic reviews of studies on TPMT genotyping or phenotyping tests in patients undergoing solid organ transplantation were identified. One study identified addressed this population and provided support for genotype analysis. In 2013, Liang et al published data on 93 heart transplant patients treated with azathioprine (AZA) (Liang, 2013). Eighty-three patients had the wild-type genotype and 10 were heterozygous for mutations. The TMPT activity level was significantly lower in the heterozygous subjects (13.1 U/mL) than in subjects with the wild-type genotype (21 U/mL RBCs; p<0.001). Moreover, there was a significantly higher rate of severe rejection in heterozygous subjects (7/10 [70%]) than in subjects with a wild-type genotype (12/83 [15%]; p<0.001). In addition, heterozygous subjects developed severe rejection earlier than wild-type subjects, at a median of 29 days versus 36 days (p=0.046). There were not statistically significant associations between TMPT genotype and the development of hepatotoxicity or leukopenia.
 
Metabolite Testing
Studies on the diagnostic accuracy of metabolite testing have focused on assessing the association between metabolite levels and disease remission or ADRs. One systematic review was identified; it focused on studies conducted in the pediatric population. In a literature search through January 4, 2013, Konidari et al identified 15 studies (total N=1026 children with IBD) (Konidari, 2014). There were 9 retrospective, 6 prospective case series, and no randomized controlled trials (RCTs). Reviewers did not pool findings. Among studies that evaluated the association between metabolite markers and clinical remission, 5 found significantly higher rates of remission with higher levels of 6-thioguanine nucleotides (6-TGN), and 6 studies did not find significant differences in 6-TGN levels between responders and nonresponders. Moreover, 5 studies found significant associations between 6-methyl-mercaptopurine ribonucleotides levels and hepatotoxicity, while 3 studies did not .
 
Several studies have considered the optimal therapeutic cutoff level of metabolites. A 2000 study by Dubinsky et al (N=92 patients) and a 2012 study by Glissen et al (N=100 patients) both found that 235 pmol/8x108 was the optimal therapeutic 6-TGN cutoff (Dubinsky, 2000; Gilissen, 2012). A 2012 Dhaliwal studied 70 patients with autoimmune hepatitis who were in remission.12 Levels of 6-TGN were significantly higher in patients who maintained remission compared with those who did not (mean, 237 pmol/8x108 vs 177 pmol/8x108, p=0.025). According to receiver operating curve analysis, a cutoff of 220 pmol/8x108 best discriminated between patients who did and did not stay in remission.
 
A 2014 study by Kopylov et al found that 6-methyl-mercaptopurine (6-MMP)/6-TGN ratios performed better than 6-TGN levels for predicting relapse in pediatric patients with Crohn disease) (Kopylov, 2014). The study included 237 patients treated with a thiopurine for at least 3 months. A total of 7.7% were TPMT heterozygous; none was TPMT homozygous. Patients were followed for 18 months; mercaptopurine (6-MP) metabolite concentration levels were measured every 3 to 4 months, or at the time of a clinical relapse or adverse event. The investigators found that 6-MMP/6-TGN ratios between 4 and 24 were significantly protective against relapse. 6-TGN levels alone were not significantly associated with relapse rates.
 
Section Summary: Diagnostic Performance
Systematic reviews show a pooled sensitivity of about 80% and specificity near 100% for identifying patients with subnormal enzymatic activity. In addition, studies have found a greater likelihood of adverse drug reactions with low TPMT activity. The evidence is limited by relatively small numbers of events and wide confidence intervals. The association between metabolite markers and adverse drug events is less consistent.
 
IMPROVEMENT IN HEALTH OUTCOMES
The use of pharmacogenomics and thiopurine metabolite testing creates the possibility of tailoring a drug regimen for each patient, with the ultimate goal of attaining disease remission and eliminating steroid therapy. The preferred study design would compare patient management (eg, drug choice) and health outcomes in patients managed with and without testing.
 
Pharmacogenomics
In 2015, Coenen et al published results of the TOPIC trial, which randomized 761 patients with IBD across 30 centers to receive standard treatment or pretreatment screening for 1 of 3 common TPMT genotype variants, followed by reduced thiopurine (AZA or 6-MP) treatment doses if patients were found to be heterozygous or homozygous carriers (Coenen, 2015). For the trial’s primary outcome, hematologic ADRs, there were no significant differences in rates over the 20-week study period between the intervention group (n=405) and the control group (n=378) (7.4% vs 7.9%; relative risk [RR], 0.93; 95% CI, 0.57 to 1.52). However, a significantly smaller proportion of TPMT carriers in the intervention (testing) group developed hematologic ADRs (2.6%) than those in the control group (22.9%; RR=0.11; 95% CI, 0.01 to 0.85).
 
Another controlled trial, known as TARGET, randomized 333 patients to receive TPMT genotyping or usual care (no genotyping) before AZA therapy (Newman, 2011). Study eligibility included age 16 years or older with a diagnosis of IBD. In the testing arm, results were generated within 1 week, and the study clinician informed. Clinicians were advised to recommend the following: maintenance dose of AZA (ie, 1.5-3 mg/kg/d) for patients with wild-type TPMT, low-dose AZA (ie, 25-50 mg/d) titrated to a maintenance dose for patients with heterozygous TPMT variant alleles, and an alternative therapy (no AZA) for patients homozygous for TPMT variant alleles. All final treatment decisions were at the discretion of the individual provider (ie, this was a pragmatic RCT). Genotyping was also done on samples from patients in the control group, but results were not made available until the end of the study.
 
Data were available for 322 (97%) of 333 patients at 4 months. The primary trial end point was stopping AZA at any ADR in the first 4 months of treatment. At 4 months, 91 (28%) of 322 patients had stopped taking AZA because of an ADR, 47 (29%) of 163 in the genotyping group and 44 (28%) of 159 in the non-genotyping group. The difference between groups was not statistically significant (p=0.74). In the genotyping arm, the average starting dose of AZA was significantly lower in TPMT heterozygote than wild-type patients (p=0.008), suggesting that clinicians followed dosing recommendations. However, at 4 months, the mean dose was similar across both arms (1.68 mg/kg/d, p=0.25), and there was no difference in dose between patients heterozygous or wild type for TPMT variant alleles (p=0.99). Moreover, at 4 months, there was no significant difference between groups in the level of clinical symptoms. For example, mean Harvey-Bradshaw Index score was 4.5 in each group (p=0.80) (54 patients in the genotyping group and 56 patients in the non-genotyping group were included in this analysis). It is important to note that this study included few patients with non-wild-type gene variants (7 heterozygous patients in the genotyping group; 2 heterozygous patients and 1 homozygous patient in the non-genotyping group). Thus, the study was underpowered to evaluate the impact of TPMT genotyping on patients with variant alleles.
 
Several prospective studies have examined variations in the efficacy of medication by patient TPTM status. For example, in a study that involved 131 patients with IBD, investigators from Europe did not find that the choice of AZA or 6-MP dose based on RBC TPMT activity prevented myelotoxicity; no patients in this study exhibited low activity (Gisbert, 2006). In a 2008 study from New Zealand, Gardiner et al noted that initial target doses to attain therapeutic levels in patients with IBD ranged from 1 to 3 mg/kg/d in intermediate (heterozygous) and normal (wild-type) metabolizers (Gardiner, 2008). This conclusion was based on analysis of 52 patients with IBD who were started on AZA or 6-MP and followed up for 9 months while 6-TGN levels and clinical status were evaluated. This study suggests that knowledge of TPMT activity can assist with initial dosing. In a study from Europe that included 394 patients with IBD, Gisbert et al found the probability of myelotoxicity was 14.3% in the TPMT intermediate group compared with 3.5% in groups with high (wild-type) activity (Gisbert, 2006). Authors concluded that determining TPMT activity before initiating treatment with AZA could minimize the risk of myelotoxicity.
 
Metabolite Testing
No prospective comparative trials identified compared use of metabolite markers with current approaches to care. In 2013, Kennedy et al retrospectively reviewed medical records of patients who had undergone metabolite testing in South Australia (Kennedy, 2013). The analysis reported on 151 patients with IBD who had been taking a thiopurine for at least 4 weeks, underwent at least 1 metabolite test, and were managed at a study site. The 151 patients had a total of 157 tests. Eighty (51%) of 157 tests were done because of flare or lack of medication efficacy, 18 (12%) were for adverse events, and 54 (34%) tests were routine. Forty-four (55%) of the 80 patients who had a metabolite test due to flare or lack of efficacy had better outcomes after the test was performed. Outcomes also improved after testing for 5 (28%) of 18 patients with an ADR to a thiopurine. For patients who had routine metabolite tests, 7 (13%) of 54 had better outcomes following testing. The rate of benefit was significantly higher in patients tested because of flare or lack of efficacy compared with those who underwent routine metabolite testing (p<0.001). Changes in patient management included medication dose adjustments, change in medication, and surgical treatment. The study lacked a control group and thus, outcomes cannot be compared to patients managed without metabolite testing. It is possible that, even in the absence of metabolite testing, patients who were not seeing a benefit or who were experiencing ADRs would have had their treatments adjusted, which could have improved outcomes.
 
Other relevant studies have examined the association between drug dose and the level of metabolite markers. In general, studies have reported that there is only weak correlation between metabolite levels and drug dose (Morales, 2007). One 2013 retrospective study, however, found a positive correlation between levels of 6-TGN and 6-MMP and weight-based AZA dose in children with IBD (Nguyen, 2013). In addition, studies have reported that levels obtained with testing are often outside of the therapeutic range. For example, Gearry et al reported that 41% of values were within the therapeutic range (Gearry, 2005) and Armstrong et al found that 32% of values were within therapeutic levels (Armstrong, 2011).
 
SUMMARY OF EVIDENCE
For individuals who are treated with thiopurines who receive thiopurine methyltransferase (TPMT) pharmacogenomics analysis or TPMT phenotype analysis, the evidence includes studies of diagnostic performance, systematic reviews, and randomized controlled trials (RCTs). Relevant outcomes are symptoms, morbid events, and change in disease status. A large number of studies have assessed the diagnostic performance of TMPT genotyping and phenotyping tests. A meta-analysis found a pooled sensitivity of about 80% and specificity near 100% for identifying patients with subnormal enzymatic activity. In addition, studies have found a greater likelihood of adverse drug reactions with low TPMT activity. One RCT reporting on health outcomes was identified; this trial did not find a significant difference in outcomes for patients managed with and without TPMT genotype testing; it may have been underpowered. The evidence is sufficient to determine that the technology results in a meaningful improvement in the net health outcome.
 
For individuals who are treated with thiopurines who receive azathioprine and/or 6-mercaptoprine metabolites analysis, the evidence includes a systematic review as well as prospective and retrospective studies. Relevant outcomes are symptoms, morbid events, and change in disease status. There is insufficient evidence from prospective studies to determine whether metabolite markers will lead to improved outcomes (primarily improved disease control and/or less adverse drug effects). Findings of studies evaluating the association between metabolite markers and clinical remission are mixed, and no prospective comparative trials have compared health outcomes in patients managed with metabolite markers and with current approaches to care. The evidence is insufficient to determine the effects of the technology on health outcomes.
 
PRACTICE GUIDELINES AND POSITION STATEMENTS
 
National Comprehensive Cancer Network
National Comprehensive Cancer Network (v.2.2016) (NCCN, 2016) guidelines on acute lymphoblastic leukemia state that testing for thiopurine methyltransferase (TPMT) gene polymorphisms should be considered for patients receiving mercaptopurine (6-MP), in particular patients who develop severe neutropenia on 6-MP (NCCN, 2016).
 
North American Society for Pediatric Gastroenterology, Hepatology and Nutrition
In 2013, the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition on inflammatory bowel disease (IBD) published consensus recommendations on the role of the TMPT enzyme and thiopurine metabolite testing in pediatric IBD (Benkov, 2013). Recommendations (high and moderate) included:
 
1. “TPMT testing is recommended before initiation of TPs [thiopurines] to identify individuals who are homozygous recessive or have extremely low TPMT activity…
 
2. Individuals who are homozygous recessive or have extremely low TPMT activity should avoid use of TPs because of concerns for significant leucopenia.
 
3. … All individuals on TPs should have routine monitoring of CBC [complete blood cell] and WBC [white blood cell] counts to evaluate for leucopenia regardless of TPMT testing results.
 
4. Metabolite testing can be used to determine adherence to TP therapy.
 
5. Metabolite testing can be used to guide dosing increases or modifications in patients with active disease….
 
6. Routine and repeat metabolite testing has little or no role in patients who are doing well and taking an acceptable dose of a TP.”
 
Association of Dermatologists
The 2011 guidelines from the British Association of Dermatologists addressed the safe and effective prescribing of azathioprine for the management of autoimmune and inflammatory skin diseases (Meggitt, 2011). The guidelines included the following recommendations on analysis of TMPT activity and azathioprine toxicity:
 
    • “There is strong evidence that baseline testing predicts severe neutropenia in patients with absent TMPT activity.
 
    • There is good evidence that intermediate TMPT activity is associated with myelotoxicity in patients using conventional azathioprine doses.
 
    • TMPT testing only identifies … haematological toxicity, hence the continued need for regular monitoring of blood counts irrespective of TMPT status.”
 
National Academy of Clinical Biochemistry
The 2010 guidelines from the National Academy of Clinical Biochemistry (NACB) stated: “thiopurine methyltransferase (TPMT) genotyping is recommended as a useful adjunct to a regimen for prescribing azathioprine” (National Academy of Clilnical Biochemistry, 2010). This A-I recommendation indicated that NACB strongly recommended adoption. The recommendation was based on evidence with consistent results from well-designed and well-conducted studies in representative populations.
 
American Gastroenterological Association
A 2006 position statement from the American Gastroenterological Association on the treatment of IBD included the following recommendations(Lichtenstein, 2006):
 
    • “Current FDA [U.S. Food and Drug Administration] recommendations suggest that individuals should have TPMT [thiopurine methyltransferase] genotype or phenotype assessed before initiation of therapy with AZA [azathioprine] or 6-MP [mercaptopurine] in an effort to detect individuals who have low enzyme activity (or who are homozygous deficient in TPMT) in an effort to avoid AZA or 6-MP therapy … and thus avoid potential adverse events. (Grade B)
 
    • Individuals who have intermediate or normal TPMT activity (wild type or heterozygotes) need measurement of frequent complete blood counts (as above) in addition to TPMT assessment because these individuals may still develop myelosuppression subsequent to use of AZA or 6-MP. (Grade B)”
 
    • “Thiopurine metabolite monitoring in the treatment of patients with 6-MP or AZA is useful when attempting to determine medical noncompliance and may be helpful for optimizing dose and monitoring for toxicity. (Grade C)”
  
2019 Update
A literature search was conducted through March 2019.  There was no new information identified that would prompt a change in the coverage statement.  The key identified literature is summarized below.
 
Friedman et al conducted a multicenter RCT in which 73 patients with clinically active or steroid-dependent IBD were randomized to 2 different doses of adjunctive allopurinol with thiopurine (azathioprine or mercaptopurine) therapy (Friedman, 2018). The purpose of the trial was to compare the efficacy of the 2 different doses of allopurinol (50 mg or 100 mg), as the thiopurine dose was modified based on metabolite testing at 4, 12, and 18 weeks. The modifications in dosing were aimed at achieving a therapeutic level of more than 260 pmol/8´108red blood cells. The primary outcome was the proportion of patients in steroid-free clinical remission at 24 weeks.
 
Garritsen et al measured thiopurine metabolite levels in patients with atopic dermatitis and/or chronic dermatitis during maintenance (n=32) and dose escalation (n=8) (Garritsen, 2018). The patient population included both high and intermediate activity genotypes and 6-TGN metabolite levels varied widely, from 42 to 696 pmol/8´108red blood cells. Interpretation of results is limited due to the small sample size and the heterogeneity in patient genotypes and drug doses.
 
Meijer et al retrospectively reviewed the charts of 24 patients with 6-MMP-induced leukocytopenia (Meijer, 2017). The authors reported that patients’ symptoms resolved on altering the treatment regimens. However, due to the retrospective nature of the study, the altering of treatment regimens cannot be attributed directly to metabolite testing.
 
Goldberg et al retrospectively reviewed medical records of patients (N=169) with IBD who were treated with thiopurines for at least 4 weeks (Goldberg, 2016). Metabolite levels of 6-TGN showed 52% were subtherapeutic, 34% were therapeutic, and 14% were supratherapeutic. Among patients who experienced active disease despite therapy, 86% were managed differently following metabolite testing. Clinical outcomes following the management changes were not reported.
 
Smith et al retrospectively reviewed medical records of 189 patients with IBD who had 6-TGN metabolite monitoring during thiopurine treatment (Smith, 2013). When 6-TGN concentrations were below the therapeutic range (n=47), 18 of the patients were given dose increases and 2 patients were given a combination of allopurinol with azathioprine. When 6-TGN concentrations were above the upper limit of the therapeutic range (n=55), 14 of the patients were given dose reductions. When nonresponders (n=53) were identified, 74% underwent treatment changes including dose increases, switching to a treatment combination of allopurinol and azathioprine or methotrexate, or surgery. Clinical outcomes related to the management changes were not reported.
 
2020 Update
A literature search was conducted through March 2020.  There was no new information identified that would prompt a change in the coverage statement.  
 
2021 Update
Annual policy review completed with a literature search using the MEDLINE database through March 2021. No new literature was identified that would prompt a change in the coverage statement. The key identified literature is summarized below.
 
The American Gastroenterological Association published a systematic review on the role of therapeutic drug monitoring in the management of inflammatory bowel diseases in 2017 (Vande Casteele, 2017). The authors did not identify any randomized trials or prospective comparative studies in thiopurine treated IBD patients comparing reactive therapeutic drug monitoring to guide treatment changes vs empiric treatment changes. Two small, randomized studies that evaluated routine therapeutic drug monitoring to guide thiopurine dosing compared to empiric weight-based dosing were identified.
 
The first was a double-blind RCT conducted in the United States using TPMT phenotype testing to guide initial dosing, followed by prospective 6-TGN guided dose adaptation compared with empiric weight-based dosing with gradual dose escalation if well tolerated (regardless of TPMT activity) in control arm (Dassopoulos, 2014). The second RCT was an open-label randomized trial conducted in Germany which investigated scheduled thiopurine metabolite testing with successive adaptation of azathiopurine therapy to a target 6-TGN concentration of 250 to 400 pmol/8 X 108 RBCs vs standard AZA weight based dosing (2.5 mg/kg body weight) (Reinshagen, 2007). Both studies were terminated early due to slow recruitment and failure to meet prespecified enrollment targets. Additionally, there was a high attrition rate in both trials (33% to 46%), although the analyses were conducted in intention-to-treat manner with worst-case scenario imputation. In the pooled analysis of both trials reported in the systematic review, there was a numerically higher proportion of patients achieving clinical remission in patients who underwent routine therapeutic drug monitoring (TDM)-guided dose adaptation compared with standard weight-based dosing (21 of 50 [42%] vs 18 of 57 [31.6%]) at 16 weeks, but the difference was not statistically significant (RR, 1.44; 95% CI, 0.59 to 3.52). The rate of serious adverse events (requiring discontinuation of therapy) was comparable between the 2 arms (TDM-guided dose adaptation vs empiric dosing: 16 of 50 [32.0%] vs 15 of 57 [26.3%]; RR, 1.20; 95% CI, 0.50 to 2.91). The systematic review concluded overall quality of evidence as very low quality (Vande Casteele, 2017).
 
2022 Update
Annual policy review completed with a literature search using the MEDLINE database through March 2022. No new literature was identified that would prompt a change in the coverage statement.

CPT/HCPCS:
0034UTPMT (thiopurine S methyltransferase), NUDT15 (nudix hydroxylase 15) (eg, thiopurine metabolism) gene analysis, common variants (ie, TPMT *2, *3A, *3B, *3C, *4, *5, *6, *8, *12; NUDT15 *3, *4, *5)
0169UNUDT15 (nudix hydrolase 15) and TPMT (thiopurine S methyltransferase) (eg, drug metabolism) gene analysis, common variants
0286UCEP72 (centrosomal protein, 72 KDa), NUDT15 (nudix hydrolase 15) and TPMT (thiopurine S methyltransferase) (eg, drug metabolism) gene analysis, common variants
81335TPMT (thiopurine S methyltransferase) (eg, drug metabolism), gene analysis, common variants (eg, *2, *3)
81401Molecular pathology procedure, Level 2 (eg, 2-10 SNPs, 1 methylated variant, or 1 somatic variant [typically using nonsequencing target variant analysis], or detection of a dynamic mutation disorder/triplet repeat) ABCC8 (ATP-binding cassette, sub-family C [CFTR/MRP], member 8) (eg, familial hyperinsulinism), common variants (eg, c.3898-9G&gt;A [c.3992-9G&gt;A], F1388del) ABL1 (ABL proto-oncogene 1, non-receptor tyrosine kinase) (eg, acquired imatinib resistance), T315I variant ACADM (acyl-CoA dehydrogenase, C-4 to C-12 straight chain, MCAD) (eg, medium chain acyl dehydrogenase deficiency), commons variants (eg, K304E, Y42H) ADRB2 (adrenergic beta-2 receptor surface) (eg, drug metabolism), common variants (eg, G16R, Q27E) APOB (apolipoprotein B) (eg, familial hypercholesterolemia type B), common variants (eg, R3500Q, R3500W) APOE (apolipoprotein E) (eg, hyperlipoproteinemia type III, cardiovascular disease, Alzheimer disease), common variants (eg, *2, *3, *4) CBFB/MYH11 (inv(16)) (eg, acute myeloid leukemia), qualitative, and quantitative, if performed CBS (cystathionine-beta-synthase) (eg, homocystinuria, cystathionine beta-synthase deficiency), common variants (eg, I278T, G307S) CFH/ARMS2 (complement factor H/age-related maculopathy susceptibility 2) (eg, macular degeneration), common variants (eg, Y402H [CFH], A69S [ARMS2]) DEK/NUP214 (t(6;9)) (eg, acute myeloid leukemia), translocation analysis, qualitative, and quantitative, if performed E2A/PBX1 (t(1;19)) (eg, acute lymphocytic leukemia), translocation analysis, qualitative, and quantitative, if performed EML4/ALK (inv(2)) (eg, non-small cell lung cancer), translocation or inversion analysis ETV6/RUNX1 (t(12;21)) (eg, acute lymphocytic leukemia), translocation analysis, qualitative, and quantitative, if performed EWSR1/ATF1 (t(12;22)) (eg, clear cell sarcoma), translocation analysis, qualitative, and quantitative, if performed EWSR1/ERG (t(21;22)) (eg, Ewing sarcoma/peripheral neuroectodermal tumor), translocation analysis, qualitative, and quantitative, if performed EWSR1/FLI1 (t(11;22)) (eg, Ewing sarcoma/peripheral neuroectodermal tumor), translocation analysis, qualitative, and quantitative, if performed EWSR1/WT1 (t(11;22)) (eg, desmoplastic small round cell tumor), translocation analysis, qualitative, and quantitative, if performed F11 (coagulation factor XI) (eg, coagulation disorder), common variants (eg, E117X [Type II], F283L [Type III], IVS14del14, and IVS14+1G&gt;A [Type I]) FGFR3 (fibroblast growth factor receptor 3) (eg, achondroplasia, hypochondroplasia), common variants (eg, 1138G&gt;A, 1138G&gt;C, 1620C&gt;A, 1620C&gt;G) FIP1L1/PDGFRA (del[4q12]) (eg, imatinib-sensitive chronic eosinophilic leukemia), qualitative, and quantitative, if performed FLG (filaggrin) (eg, ichthyosis vulgaris), common variants (eg, R501X, 2282del4, R2447X, S3247X, 3702delG) FOXO1/PAX3 (t(2;13)) (eg, alveolar rhabdomyosarcoma), translocation analysis, qualitative, and quantitative, if performed FOXO1/PAX7 (t(1;13)) (eg, alveolar rhabdomyosarcoma), translocation analysis, qualitative, and quantitative, if performed FUS/DDIT3 (t(12;16)) (eg, myxoid liposarcoma), translocation analysis, qualitative, and quantitative, if performed GALC (galactosylceramidase) (eg, Krabbe disease), common variants (eg, c.857G&gt;A, 30-kb deletion) GALT (galactose-1-phosphate uridylyltransferase) (eg, galactosemia), common variants (eg, Q188R, S135L, K285N, T138M, L195P, Y209C, IVS2-2A&gt;G, P171S, del5kb, N314D, L218L/N314D) H19 (imprinted maternally expressed transcript [non-protein coding]) (eg, Beckwith-Wiedemann syndrome), methylation analysis IGH@/BCL2 (t(14;18)) (eg, follicular lymphoma), translocation analysis; single breakpoint (eg, major breakpoint region [MBR] or minor cluster region [mcr]), qualitative or quantitative (When both MBR and mcr breakpoints are performed, use 81278) KCNQ1OT1 (KCNQ1 overlapping transcript 1 [non-protein coding]) (eg, Beckwith-Wiedemann syndrome), methylation analysis LINC00518 (long intergenic non-protein coding RNA 518) (eg, melanoma), expression analysis LRRK2 (leucine-rich repeat kinase 2) (eg, Parkinson disease), common variants (eg, R1441G, G2019S, I2020T) MED12 (mediator complex subunit 12) (eg, FG syndrome type 1, Lujan syndrome), common variants (eg, R961W, N1007S) MEG3/DLK1 (maternally expressed 3 [non-protein coding]/delta-like 1 homolog [Drosophila]) (eg, intrauterine growth retardation), methylation analysis MLL/AFF1 (t(4;11)) (eg, acute lymphoblastic leukemia), translocation analysis, qualitative, and quantitative, if performed MLL/MLLT3 (t(9;11)) (eg, acute myeloid leukemia), translocation analysis, qualitative, and quantitative, if performed MT-ATP6 (mitochondrially encoded ATP synthase 6) (eg, neuropathy with ataxia and retinitis pigmentosa [NARP], Leigh syndrome), common variants (eg, m.8993T&gt;G, m.8993T&gt;C) MT-ND4, MT-ND6 (mitochondrially encoded NADH dehydrogenase 4, mitochondrially encoded NADH dehydrogenase 6) (eg, Leber hereditary optic neuropathy [LHON]), common variants (eg, m.11778G&gt;A, m.3460G&gt;A, m.14484T&gt;C) MT-ND5 (mitochondrially encoded tRNA leucine 1 [UUA/G], mitochondrially encoded NADH dehydrogenase 5) (eg, mitochondrial encephalopathy with lactic acidosis and stroke-like episodes [MELAS]), common variants (eg, m.3243A&gt;G, m.3271T&gt;C, m.3252A&gt;G, m.13513G&gt;A) MT-RNR1 (mitochondrially encoded 12S RNA) (eg, nonsyndromic hearing loss), common variants (eg, m.1555A&gt;G, m.1494C&gt;T) MT-TK (mitochondrially encoded tRNA lysine) (eg, myoclonic epilepsy with ragged-red fibers [MERRF]), common variants (eg, m.8344A&gt;G, m.8356T&gt;C) MT-TL1 (mitochondrially encoded tRNA leucine 1 [UUA/G]) (eg, diabetes and hearing loss), common variants (eg, m.3243A&gt;G, m.14709 T&gt;C) MT-TL1 MT-TS1, MT-RNR1 (mitochondrially encoded tRNA serine 1 [UCN], mitochondrially encoded 12S RNA) (eg, nonsyndromic sensorineural deafness [including aminoglycoside-induced nonsyndromic deafness]), common variants (eg, m.7445A&gt;G, m.1555A&gt;G) MUTYH (mutY homolog [E. coli]) (eg, MYH-associated polyposis), common variants (eg, Y165C, G382D) NOD2 (nucleotide-binding oligomerization domain containing 2) (eg, Crohn's disease, Blau syndrome), common variants (eg, SNP 8, SNP 12, SNP 13) NPM1/ALK (t(2;5)) (eg, anaplastic large cell lymphoma), translocation analysis PAX8/PPARG (t(2;3) (q13;p25)) (eg, follicular thyroid carcinoma), translocation analysis PRAME (preferentially expressed antigen in melanoma) (eg, melanoma), expression analysis PRSS1 (protease, serine, 1 [trypsin 1]) (eg, hereditary pancreatitis), common variants (eg, N29I, A16V, R122H) PYGM (phosphorylase, glycogen, muscle) (eg, glycogen storage disease type V, McArdle disease), common variants (eg, R50X, G205S) RUNX1/RUNX1T1 (t(8;21)) (eg, acute myeloid leukemia) translocation analysis, qualitative, and quantitative, if performed SS18/SSX1 (t(X;18)) (eg, synovial sarcoma), translocation analysis, qualitative, and quantitative, if performed SS18/SSX2 (t(X;18)) (eg, synovial sarcoma), translocation analysis, qualitative, and quantitative, if performed VWF (von Willebrand factor) (eg, von Willebrand disease type 2N), common variants (eg, T791M, R816W, R854Q)

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