Thiopurine metabolism (TPMT and NUDT15 genes)

Thiopurine drugs such as azathioprine are handled by two genes, TPMT and NUDT15. Doctors combine both into one dosing recommendation, driven by whichever shows more reduced function.

Possible results

Normal thiopurine metabolism. You don't carry the tested reduced-function TPMT or NUDT15 variants, so from what these genes show you break down thiopurine medications normally.

Reduced thiopurine metabolism. You carry one reduced-function copy in TPMT or NUDT15, so thiopurine drugs hit you harder. If prescribed, a lower starting dose is usually recommended to avoid a dangerous drop in blood counts.

Poor thiopurine metabolism. One of your thiopurine genes (TPMT or NUDT15) has two reduced-function copies, so standard thiopurine doses can cause severe drops in blood cells. Doctors usually avoid these drugs or use much lower doses for this genotype.

Evidence & sources

This panel reads TPMT*3C, TPMT*2, NUDT15*3.

Reads the most common reduced-function versions of TPMT and NUDT15. Some rarer reduced versions of these genes are not tested, so a 'normal' result does not fully exclude reduced metabolism.

CPIC provides dosing guidance for azathioprine based on this gene.

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