Also known as: Gilbert syndrome, Irinotecan toxicity« Back to test list
The UGT1A1 gene encodes an enzyme responsible for conjugation of bilirubin in the liver. Variants in UGT1A1 can impair this process, resulting in mild unconjugated hyperbilirubinaemia in the absence of liver disease or overt haemolysis, referred to as Gilbert syndrome.
Gilbert syndrome is an autosomal recessive condition, and therefore detection of two variants that result in reduced function of UGT1A1 is required for a diagnosis. A specific variant, described as the UGT1A1*28 allele (an insertion of a TA in the TA repeat region of the UGT1A1 gene promoter) is the most common cause of Gilbert syndrome in Caucasian populations; in other populations, variants outside the promoter region have been detected more frequently.
Conjugation is also an important step in elimination of drugs, and therefore individuals with Gilbert syndrome may have increased susceptibility to adverse effects of some drugs metabolised by UGT1A1, such as indinavir, atazanavir and irinotecan.
Gilbert syndrome is a benign condition, but diagnosis can be helpful in avoiding the pursuit of other more serious causes of elevated bilirubin.
This test has a role in identifying patients who may benefit from avoiding a specific drug or dose. Other clinical factors, including concurrent medications, should be considered when using results from this test to determine drug dosage.
Analysis of the UGT1A1 gene for *36, *1, *28 and *37 allele variants (corresponding to TA repeat numbers of 5, 6, 7 and 8, respectively). UGT1A1 variants outside the TA repeat region are not detected.
This test can be requested by any medical practitioner.
4 mL blood in EDTA (separate tube required). Specimens may be collected by the requesting practitioner or at any Sonic Healthcare pathology collection centre.
To help ensure the quality of the test, a genetic test should be done with a dedicated sample whenever possible i.e. a sample collected specifically for that test rather than a sample that is used for multiple tests.
We also recommend that the patient or another adult check the labelling of request forms and sample tubes.
Please indicate whether the testing is for Gilbert syndrome or drug sensitivity, and list current and proposed medications, on the request form.