Thiopurine Metabolites

Test ID:

703983

CPT code:

80299

Synonyms:

Thiopurine Metabolites
6MP Metabolites
6TG Metabolites
Azathioprine Metabolites
Mercaptopurine Metabolites

Clinical 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:
1. 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.
2. Clinically responsive patients to look for excessive levels of either 6-MMP or 6-TG to avoid toxicity.

Test Information:

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.