Currentblue cross blue shield - tennesseePolicy N/A

Metabolite Markers of Thiopurines Testing

Defines coverage criteria and limitations for phenotypic TPMT testing and monitoring of thiopurine metabolite markers (6-TGN, 6-MMP/6-MMRP) for members receiving or considered for azathioprine, mercaptopurine, or thioguanine therapy, including indications in IBD and ALL; includes noncoverage statements for other uses.

Policy Summary

Payerblue cross blue shield - tennessee

PolicyMetabolite Markers of Thiopurines Testing

Policy CodePolicy N/A

Change TypeAdministrative adoption note

Effective DateJul 1, 2023

Next Review Date

Key ActionConfirm member's benefit coverage at time of request; coverage depends on the individual's benefit plan and Medicare/Medicaid specifications.

SourceLink

POLICY UPDATE CHANGES

Effective date noted: Adopted Avalon policy recommendation effective 7/1/2023.

3Covered clinical scenarios listed

2Not-covered test categories

3Key metabolites / enzymes referenced

Coverage Summary

This policy defines coverage criteria and limitations for one-time phenotypic TPMT testing and for monitoring thiopurine metabolite markers (including 6-TGN and 6-MMRP/6-MMP) for members receiving or being considered for thiopurine therapy (azathioprine, 6-mercaptopurine, 6-thioguanine). It specifically addresses indications in inflammatory bowel disease (IBD) and acute lymphoblastic leukemia (ALL) and takes a mixed coverage stance—listing covered scenarios for TPMT phenotype assessment and reactive metabolite monitoring while excluding other uses not specified in the covered indications.

Key thresholds and quick facts

6-TGN therapeutic range (example)230-400 pmol/8 x 10^8 erythrocytes (literature cited)

6-TGN toxicity threshold>400 pmol/8 x 10^8 erythrocytes associated with marrow toxicity (literature cited)

NUDT15 genotype-stratified cut-offs (Zhu et al., 2019)CT ~319.2 pmol/8 × 10^8 RBC; CC ~411.5 pmol/8 × 10^8 RBC

Covered clinical scenarios listed3

Not-covered test categories2

Key metabolites/enzymes referencedTPMT, 6-TGN, 6-MMP/6-MMRP, NUDT15 (3+ referenced)

One-time TPMT phenotypic testing covered whenPrior to initiating AZA/6-MP/6-TG or for abnormal CBC not responsive to dose reduction

Medical-Necessity Criteria

Covered / Meets Coverage Criteria

Phenotypic TPMT testing or thiopurine metabolite monitoring MEETS COVERAGE CRITERIA when ALL of the following apply as specified in subitems:

One-time phenotypic analysis of TPMT
- In patients prior to initiating treatment with azathioprine (AZA), mercaptopurine (6-MP) or thioguanine (6-TG).
- In patients on thiopurine therapy with abnormal complete blood count (CBC) results that do not respond to dose reduction.
Thiopurine metabolite monitoring in inflammatory bowel disease (IBD)
- To measure blood levels in individuals suspected of having toxic responses to AZA and/or 6-MP (e.g., hepatotoxicity or myelotoxicity).
- To measure drug levels in individuals who have not responded to therapy (e.g., persistent fever, further weight loss, and bloody diarrhea).
Thiopurine metabolite monitoring in acute lymphoblastic leukemia (ALL)
- For patients showing signs of a lack of myelosuppression while on therapy.
- For patients who do not tolerate thiopurines.

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Not Covered / Does Not Meet Coverage Criteria

The following testing DOES NOT MEET COVERAGE CRITERIA in all other situations not specified above:

Phenotypic analysis of the enzyme TPMT in situations other than the listed covered indications (see Covered).
Analysis of the metabolite markers of azathioprine and 6-mercaptopurine, including 6-methylmercaptopurine ribonucleotides (6-MMRP) and 6-thioguanine nucleotides (6-TGN), in situations other than the listed covered indications.

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Provider Actions & Documentation

Documentation Required

Apply benefit determination

Confirm member's benefit coverage at time of request; coverage is dependent on individual's benefit plan and Medicare/Medicaid specifications.

Documentation Required

Indication documentation for covered testing

For TPMT phenotypic testing: document either planned initiation of AZA/6-MP/6-TG or abnormal CBC not responsive to dose reduction; for metabolite monitoring in IBD or ALL: document suspected toxicity, nonresponse, lack of myelosuppression, or intolerance as applicable.

Planned initiation of azathioprine (AZA), 6-mercaptopurine (6-MP), or 6-thioguanine (6-TG)
Abnormal complete blood count (CBC) not responsive to dose reduction
Suspected toxicity (e.g., hepatotoxicity or myelotoxicity)
Nonresponse to therapy (e.g., persistent fever, further weight loss, bloody diarrhea)
Lack of myelosuppression
Intolerance to thiopurines

Documentation Required

Concurrent testing guidance

Consider TPMT and NUDT15 genotype/phenotype assessment when clinically indicated; TPMT testing does not replace routine CBC and LFT monitoring.

Background & Evidence

Thiopurine drugs (AZA, 6-MP, 6-TG) have complex metabolism and patient responses vary widely; downstream metabolites such as 6-TGN and 6-MMP/6-MMRP are associated with both efficacy and toxicities (hepatotoxicity, bone marrow toxicity). TPMT enzyme activity is a major determinant of AZA and 6-MP metabolism and influences 6-TGN and 6-MMP levels; measuring TPMT activity prior to initiating therapy may help identify individuals at risk for severe dose-dependent myelosuppression or who may require dose adjustment. NUDT15 variants also affect thiopurine tolerance and are particularly relevant in some populations (eg, East Asian) where poor metabolizer phenotypes are more common.

Therapeutic drug monitoring (measurement of thiopurine metabolites) can guide clinical management in cases of suspected toxicity or nonresponse—helping distinguish nonadherence, underdosing, hypermetabolism, or toxic metabolite profiles—and is recommended in reactive situations for IBD and in ALL when lack of myelosuppression, intolerance, or suspected toxicity occur. Evidence links higher 6-TGN levels with increased odds of remission in IBD, and studies have proposed therapeutic and toxicity thresholds to aid interpretation.

Evidence item	Summary
Association between 6-TGN and remission	Multiple studies and meta-analyses report higher 6-TGN levels associated with increased odds of remission in IBD; example thresholds ~230-250 pmol/8x10^8 RBC with pooled odds ratios for remission (eg OR 2.25 at 235 pmol and OR 4.71 at 250 pmol) and a pooled mean difference ~63 pmol/8x10^8 RBC.
TPMT variant prevalence	Majority have normal TPMT activity; ~11% are heterozygous with low activity and ~0.3% have negligible activity; TPMT influences dosing and pre-treatment TPMT measurement may help prevent toxicity.
NUDT15 impact	NUDT15 poor metabolizer phenotype more common in East Asian populations (up to ~1 in 50) and is associated with severe leukopenia; genotype-stratified 6-TGN cut-offs (eg CT ~319.2 pmol/8x10^8 RBC, CC ~411.5 pmol/8x10^8 RBC) improve predictive sensitivity for thiopurine-induced leukopenia.

Glossary: TPMT = Thiopurine methyltransferase; NUDT15 = nudix 15 (nucleoside diphosphate-linked moiety X motif 15); 6-MMRP = 6-methyl-mercaptopurine ribonucleotides; 6-TGN = 6-thioguanine nucleotides; CBC = complete blood count.

Policy Summary

Payerblue cross blue shield - tennessee

PolicyMetabolite Markers of Thiopurines Testing

Policy CodePolicy N/A

Change TypeAdministrative adoption note

Effective DateJul 1, 2023

Next Review Date

Key ActionConfirm member's benefit coverage at time of request; coverage depends on the individual's benefit plan and Medicare/Medicaid specifications.

SourceLink

On This Page

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Metabolite Markers of Thiopurines Testing

Coverage Summary

Medical-Necessity Criteria

Coding

Provider Actions & Documentation

Background & Evidence

Revision History