Gilbert's syndrome laboratory findings
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Exclusion of other conditions
While this syndrome is considered harmless, it is clinically important because it may be confused with much more dangerous liver conditions. However, these will show other indicators of liver dysfunction:
- Hemolysis 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).
- Hepatitis can be excluded by negative blood samples for antigens specific to the different hepatitis vira.
- Cholestasis can be excluded by the absence of lactate dehydrogenase, low levels of conjugated bilirubin and ultrasound scan of the bile ducts.
- More severe types of glucoronyl transferase disorders like Crigler-Najjar syndrome (types I and II). These 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).
- Other diseases of the liver can be exluded by the liver-enzymes ALT, AST and albumin being within normal ranges.
Normal levels of total bilirubin (conjugated and unconjugated) are under 20 mmol/dL. Patients with GS show predominantly elevated unconjugated bilirubin, while conjugated is usually in normal ranges and form less than 20% of the total. Levels of bilirubin in GS patients should be between 20 mmol/dl and 80 mmol/dl (or, divided by 17.1 to express these numbers in mg/dL, between 1.17 and 4.68 mg/dL). GS patients will have a ratio of unconjugated/conjugated (indirect/direct) bilirubin that is commensurately higher than those without GS. Other liver enzymes are expected to be similar between patients with and without GS. Complete liver enzyme tests are ordered in order to assure the correct diagnosis.
The level of total bilirubin is often increased if the blood sample is taken while fasting.
More severe types of glucoronyl transferase disorders like GS are Crigler-Najjar syndrome (types I and II). These are much more severe and cause brain damage in infancy (type I) and teenage years (type II).
Findings specific to Gilbert's syndrome
Patients with GS show predominantly elevated unconjugated bilirubin, while conjugated is usually within normal ranges and form less than 20% of the total. Levels of bilirubin in GS patients is reported to be from 20 μmol/dl to 90 μmol/dl (1.2 to 5.3 mg/dL) compared to the normal amount of < 20 μmol/dL. 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 increased if the blood sample is taken after fasting for two days, and a fast can therefore be useful diagnostically. If the total bilirubin does in fact increase while fasting, the patient can then be given low doses of phenobarbital when fasting has ended, and following samples should show a decrease in total bilirubin toward normal levels.
- Piter J. Bosma, Ph.D., Jayanta Roy Chowdhury, M.D., Conny Bakker, Shailaja Gantla, Ph.D., Anita de Boer, Ben A. Oostra, Ph.D., Dick Lindhout, Ph.D., Guido N.J. Tytgat, M.D., Peter L.M. Jansen, M.D., Ph.D., Ronald P.J. Oude Elferink, Ph.D., and Namita Roy Chowdhury, Ph.D. (1995). "The Genetic Basis of the Reduced Expression of Bilirubin UDP-Glucuronosyltransferase 1 in Gilbert's Syndrome". New England Journal of Medicine. 333: 1171–1175. doi:10.1056/NEJM199511023331802. PMID 7565971.
- J L Gollan, C Bateman, B H Billing (1976). "Effect of dietary composition on the unconjugated hyperbilirubinaemia of Gilbert's syndrome". Gut. 17 (17): 335–340. doi:10.1136/gut.17.5.335. PMID 1278716.
- N Carulli, M Ponz de Leon, E Mauro, F Manenti, A Ferrari (1976). "Alteration of drug metabolism in Gilbert's syndrome". Gut. 17 (17): 581–587. doi:10.1136/gut.17.8.581. PMID 976795.