UGT1A1 Testing Before — Irinotecan

The test looks at specific positions in your UGT1A1 gene — the part of your DNA that codes for the enzyme responsible for clearing irinotecan's active compound. It identifies whether you carry variants, most commonly *28 or *6, that reduce how efficiently that enzyme works. This is a genetic test, not a routine blood count, and it is processed on a separate sample sent to a genomics or pharmacogenomics laboratory.

Your oncologist decides whether to order it based on your specific treatment regimen and clinical picture. CPIC and NCCN guidance considers UGT1A1 status clinically relevant before irinotecan-based treatment, particularly where the result could influence how treatment is planned. If you are being offered irinotecan and have not been told about this test, it is reasonable to ask your oncologist whether it applies to your case.

Your oncologist reviews the result alongside your cancer type, stage, treatment goals and overall fitness before deciding how to proceed. The result is one piece of clinical information — it does not make a treatment decision on its own. Ask your oncologist to explain in plain language what your result means for your specific plan, and what, if anything, changes because of it.

Pharmacogenomic testing for UGT1A1 is available at specialised genetics and genomics laboratories in India, including through some large diagnostic chains. It is not uniformly available at every oncology centre, and your sample may need to be sent to a reference laboratory. Ask your treating team whether they can arrange it and which laboratory they use. Availability and turnaround time vary by location.

Turnaround time depends on whether the sample is processed locally or at a reference laboratory. Results can take anywhere from a few days to two weeks. Your oncology team can give you a clearer timeline once they know which laboratory is handling the sample. If starting treatment soon matters, tell your team so the timing can be planned around the result.

Carrying a UGT1A1 variant does not automatically rule out irinotecan-based treatment. Your oncologist weighs the result against your cancer type, the available alternatives and the goals of your treatment. Many patients who carry variants go on to receive irinotecan as part of their plan. The test gives your team information before the first dose rather than a problem to discover after side effects have occurred.

Report immediately any diarrhoea that is clearly worse than your usual pattern — particularly if it is watery, frequent or comes with cramping. Fever alongside any bowel change needs same-day contact with your team, not a wait until the next appointment. Chills, feeling unusually unwell or mouth sores can indicate that your white blood cell count has fallen dangerously low and need urgent assessment. Do not take over-the-counter medicines for diarrhoea without asking your team first.

No. UGT1A1 testing predicts how safely your body can handle irinotecan, not whether it will be effective against your cancer. Effectiveness is estimated through different information — your cancer type, stage, molecular profile, and how that cancer is known to respond to this class of drug. UGT1A1 testing is a safety test, not a response test. Your oncologist can explain what separate information guides the judgement that irinotecan is likely to help you.