Diagnosis
People with GS predominantly have elevated unconjugated bilirubin, while conjugated bilirubin is usually within the normal range and is less than 20% of the total. Levels of bilirubin in GS patients are reported to be from 20 μM to 90 μM (1.2 to 5.3 mg/dL) compared to the normal amount of < 20 μM. GS patients will have a ratio of unconjugated/conjugated (indirect/direct) bilirubin that is commensurately higher than those without GS.
The level of total bilirubin is often further increased if the blood sample is taken after fasting for two days, and a fast can therefore be useful diagnostically. A further conceptual step that is rarely necessary or appropriate is to give a low dose of phenobarbital: the bilirubin will decrease substantially.
There are also tests that detect DNA mutations of UGT1A1 by polymerase chain reaction or DNA fragment sequencing.
Read more about this topic: Gilbert's Syndrome