Thiopurine Metabolites, Whole Blood

Casandra

Casandra Test Code MC75421Version 1 (DRAFT)

Performing Lab

Lab Mayo Clinic LabLab Test ID THIOCPT Code 80299

Thiopurine Metabolites, Whole Blood

Clinical Use

Use

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. 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.

Special Instructions

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

Limitations

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.

Test Details

New York Approved