Esoterix
Synonyms
6MP Metabolites 6TG Metabolites Azathioprine Metabolites Mercaptopurine Metabolites
Expected Turnaround Time
5 - 7 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Specimen Requirements
Specimen
Whole blood
Volume
3 mL
Minimum Volume
1 mL (Note: This volume does not allow for repeat testing.)
Container
Lavender-top (EDTA) tube
Collection
Collect blood in lavender-top (EDTA) tube only. Gently invert to mix. Submit whole blood refrigerated. Do not separate specimen. Do not freeze.
Storage Instructions
Ship refrigerated.
Causes for Rejection
Gross hemolysis
Test Details
Use
This assay measures the red-cell concentration of 6-MMP (formed from 6-MP by thiopurine methyltransferase) and also measures the concentration of the resulting 6-TG after removal of the mono-, di-, or tri-phosphates from the various 6-thioguanine nucleotides. Once thiopurine therapy has been undertaken and an equilibrated drug level is achieved (usually three to six months), literature suggests that the measurement of thiopurine metabolites is warranted in the following situations: Unresponsive patients to rule out (a) patient noncompliance (low 6-MMP and low 6-TG in those not taking medications), (b) those with diversion of metabolites away from 6-TG production (low 6-TG and normal or increased 6-MMP), (c) those with refractory to treatment (adequate 6-TG but lack of clinical response), and (d), those with excessive 6-MMP (or increased 6-MMP:6-TG ratio with adequate 6-TG) leading to increased hepatotoxicity. Clinically responsive patients to look for excessive levels of either 6-MMP or 6-TG to avoid toxicity.
Limitations
This test should only be performed for patients currently on thiopurine therapy. This therapy includes administration of azathioprine or mercaptopurine. This test may not be useful in patients with autoimmune hepatitis.
Methodology
Whole blood washing and red blood cell harvesting/counting. Liquid chromatography/tandem mass spectrometry (LC/MS-MS) after acidic hydrolysis.