Lengths of the TA repeat polymorphism in the promoter region of the UTG1A1 gene are determined by fragment analysis using capillary electrophoresis. The alleles detected include the common normal allele *1 (with 6 TA repeats) and the common abnormal allele *28 (7 repeats). The patient's genotype is reported along with the associated high, intermediate, or low risk for toxicity from the quinolone-based alkaloids.
Polymorphisms in the gene UGT1A1 can reduce expression of the enzyme UDP glucuronosyl transferase 1A1 and lead to toxicity from incomplete metabolism of the drug irinotecan, which is used in the treatment of colorectal and gastric cancers. There is increased risk for hematologic and gastrointestinal toxicity (especially neutropenia and diarrhea) with irinotecan therapy in patients who carry one or two copies of the abnormal allele UGT1A1*28. Testing for UGT1A1 genotype before initiating irinotecan therapy is recommended so initial doses can be adjusted. This test may also be used for diagnostic confirmation of Gilbert and Crigler-Najjar hyperbilirubinemia syndromes.
- Peripheral blood: 5 mL in EDTA tube.
Use cold pack for transport, making sure cold pack is not in direct contact with specimen.