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Test Code CHEM115 Thiopurine Metabolites, Whole Blood

Additional Codes

Y6T


Ordering Guidance


This specimen cannot be shared with testing for tacrolimus, cyclosporine, sirolimus or everolimus. Testing for these must be ordered separately and separate specimens submitted.



Shipping Instructions


Specimen must be shipped refrigerated.



Specimen Required


Container/Tube: Lavender top (EDTA)

Specimen Volume: 3 mL

Collection Instructions: Send whole blood specimen in original tube. Do not aliquot, centrifuge, or freeze.


Useful For

Aids physicians in dose adjustments, minimizing dose-dependent toxicity, and monitoring compliance of thiopurine drug therapy

Testing Algorithm

A red blood cell (RBC) count is performed followed by determination of thiopurine metabolite values by liquid chromatography tandem mass spectrometry. Values are utilized to calculate and report the final results (unit of measure: pmol/8 x 10[8] RBC) for 6-thioguanine nucleotides and 6-methylmercaptopurine derivative analyte.

 

For more information see:

-Ulcerative Colitis and Crohn Disease Therapeutic Drug Monitoring Algorithm

-TPMT Testing in the Treatment of Inflammatory Bowel Disease Algorithm

Method Name

Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

Reporting Name

Thiopurine Metabolites, B

Specimen Type

Whole Blood EDTA

Specimen Minimum Volume

1.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole Blood EDTA Refrigerated (preferred) 8 days
  Ambient  24 hours

Reject Due To

Gross hemolysis Reject
Moderate hemolysis Reject
Gross lipemia OK
Gross icterus OK
Clotted Reject

Clinical Information

This test is primarily used to verify compliance, optimize therapy, and identify elevated metabolite concentrations that may result in toxicity after initiation of thiopurine drug therapy for the treatment of inflammatory bowel disease. Recommended time points for monitoring include: 4 weeks after starting treatment to verify patient compliance and look for early risk of toxicity; 12 to 16 weeks after starting therapy when 6-thioguanine nucleotides have reached steady-state; and annually.(1) It may also be ordered in patients who do not respond to therapy as expected or as needed for dose changes, flare-ups, signs of toxicity, or suspicion of noncompliance. The test will measure 6-methylmercaptopurine and 6-thioguanine nucleotides in erythrocytes.

Reference Values

6-Thioguanine Nucleotides (6-TGN): 235-450 pmol/8x10(8) red blood cell (RBC)

6-Methylmercaptopurine (6-MMP): Less than or equal to 5700 pmol/8x10(8) RBC

Interpretation

Target 6-thioguanine concentrations are 235 to 450 pmol/8x10(8) red blood cell (RBC) with lower levels suggesting suboptimal dosing and higher levels associated with increased risk of myelotoxicity and leukopenia. High 6-methylmercaptopurine levels (greater than 5700 pmol/8x10[8] RBC) suggest an increased risk for hepatotoxicity and potentially "thiopurine hypermethylation."

Cautions

This test cannot be used to predict optimal starting dose. It is sensitive to hemolysis and transport conditions. This test does not replace monitoring of patients using other laboratory tests (eg, complete blood cell count, liver function tests).

 

Final concentrations are reported per the red blood cell (RBC) count (unit of measure =pmol/8 x 10[8] RBC) for the 6-thioguanine nucleotides and 6-methylmercaptopurine derivative analytes. Therefore, any significant lysis of the RBCs will lead to an artificially lower RBC count that could falsely increase the final concentrations. Due to this, moderately hemolyzed samples are rejected.

Method Description

Red blood cell count is first performed and then the thiopurine metabolites values are determined by mass spectrometry.(Unpublished Mayo Method)

Day(s) Performed

Monday, Wednesday, Friday

Report Available

2 to 4 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

80299

LOINC Code Information

Test ID Test Order Name Order LOINC Value
THIO Thiopurine Metabolites, B 82869-9

 

Result ID Test Result Name Result LOINC Value
49580 6-Thioguanine Nucleotides 32660-3
49581 6-Methylmercaptopurine 32654-6

Forms

If not ordering electronically, complete, print, and send Gastroenterology and Hepatology Test Request (T728) with the specimen