🧭 When to suspect

Gilbert's syndrome is a common, entirely benign inherited variation in bilirubin handling. The enzyme UDP-glucuronosyltransferase 1A1 (UGT1A1) – which conjugates bilirubin in the liver so it can be excreted – has reduced activity, so unconjugated (indirect) bilirubin accumulates and the patient becomes mildly jaundiced. The liver is otherwise structurally and functionally normal.

Suspect it in an adolescent or young adult with mild, intermittent, unconjugated hyperbilirubinaemia and no evidence of liver disease or haemolysis (breakdown of red blood cells). It is usually picked up incidentally on routine blood tests, or noticed during an illness. Jaundice is typically the only feature, and it characteristically appears or deepens at times of physiological stress – fasting, intercurrent infection, dehydration, surgery, heavy exertion, sleep deprivation, or around menstruation. Inheritance is usually autosomal recessive, men are affected roughly three times as often as women, and around 5–8% of the UK population carry the trait.

The key clinical skill is twofold: recognise the characteristic biochemical pattern, and actively exclude the mimics – Gilbert's syndrome is a diagnosis of exclusion, never a label to be applied loosely. Liver function tests (LFTs, i.e. liver blood tests) tell most of the story.

Finding	Typical pattern in Gilbert's syndrome
Bilirubin	Mildly raised and unconjugated (indirect); often < 50 µmol/L, fluctuates, and rises with fasting or illness; rarely exceeds ~85 µmol/L.
Conjugated (direct) fraction	< 30% of the total bilirubin (i.e. predominantly unconjugated).
Other liver enzymes (ALT, AST, ALP, GGT) and albumin	Normal – ALT/AST (transaminases), ALP (alkaline phosphatase) and GGT (gamma-glutamyl transferase) are all unremarkable.
Full blood count (FBC), reticulocytes, blood film	Normal – no anaemia and no features of haemolysis.
Urine dipstick for bilirubin	Negative – unconjugated bilirubin is not water-soluble, so it does not appear in urine.
The patient	An otherwise well teenager or young adult, often with a family history of mild jaundice.

Source: British Society of Gastroenterology · British Liver Trust

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