People with GS predominantly have elevated unconjugated bilirubin, while conjugated bilirubin is usually within the normal range or 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 have a ratio of unconjugated/conjugated (indirect/direct) bilirubin 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. Tests can also detect DNA variants of UGT1A1 by polymerase chain reaction or DNA fragment sequencing. Differential diagnosis While<unk><unk>  is considered harmless, it is clinically important because it may give rise to a concern about a blood or liver condition, which could be more dangerous. However, these conditions have additional indicators: * In GS, unless another disease of the liver is also present, the liver enzymes ALT/SGPT and AST/SGOT, as well as albumin, are within normal ranges. * More severe types of glucuronyl transferase disorders such as Crigler–Najjar<unk>  (types I and II) are much more severe, with 0–10% UGT1A1 activity, with sufferers at risk of brain damage in infancy (type I) and teenage years (type II). * Hemolysis of any cause can be excluded by a full blood count, haptoglobin, lactate dehydrogenase levels, and the absence of reticulocytosis (elevated reticulocytes in the blood would usually be observed in haemolytic anaemia). * Dubin–Johnson<unk>  and Rotor<unk>  are rarer autosomal recessive disorders characterized by an increase of conjugated bilirubin. * Viral hepatitis associated with increase of conjugated bilirubin can be excluded by negative blood samples for antigens specific to the different hepatitis viruses. * Cholestasis can be excluded by normal levels of bile acids in plasma, the absence of lactate dehydrogenase, low levels of conjugated bilirubin, and ultrasound scan of the bile ducts. * Vitamin B12 deficiency - elevated bilirubin levels (and MCV counts above 90-92) can be associated with a vitamin B12 deficiency.
Gilbert's syndrome
Gaucher's disease
Dubin–Johnson syndrome
Adams–Oliver syndrome
Progressive familial intrahepatic cholestasis
Biliary disease
Vanishing bile duct syndrome
Familial cirrhosis