Bilirubin

What is Bilirubin?

Bilirubin is the yellow breakdown product generated when the spleen clears old red blood cells and the haemoglobin protein is dismantled. This 'unconjugated' or indirect bilirubin is poorly water-soluble; the liver binds it to glucuronic acid to make it water-soluble (direct or conjugated bilirubin) and then excretes it via bile into the gut, where intestinal bacteria convert it further. Bilirubin is reported in µmol/L (internationally also mg/dL; 1 mg/dL ≈ 17.1 µmol/L). Standard labs measure total bilirubin; with further differentiation, direct and indirect bilirubin are measured separately. Elevated bilirubin can have three origins: excessive red cell breakdown (pre-hepatic, as in haemolytic anaemia), impaired liver processing (hepatic, as in hepatitis or cirrhosis), or obstructed bile flow (post-hepatic or cholestatic, as in gallstones or bile duct cancer). Each pattern produces a distinct profile on the liver enzyme panel, which is why bilirubin is almost always interpreted alongside ALT, AST, GGT, and ALP.

Why is Bilirubin relevant?

Bilirubin is one of the most visible liver and bile-duct markers, literally: a markedly elevated value causes jaundice (icterus) — yellow discolouration of the skin and whites of the eyes — and dark urine. Those clinical signs are a clear signal, but bilirubin also rises before jaundice becomes visible. In the blood panel it is therefore a sensitive indicator of liver pressure and bile-duct obstruction. A common and often overlooked cause of mildly elevated bilirubin is Gilbert's syndrome: a benign genetic variant in which hepatic conjugation is slightly slower. People with Gilbert's have chronically mild bilirubin elevation (typically 20–80 µmol/L), which peaks with fasting, stress, illness, or poor sleep. Gilbert's is not a disease and needs no treatment, but it is useful to know — so that a mild bilirubin elevation does not trigger unnecessary further investigation.

Bilirubin high or low — what it means

Always read bilirubin alongside ALT, AST, GGT, and ALP. An isolated raised bilirubin with normal ALT and GGT fits haemolytic anaemia (over-production) or Gilbert's (impaired conjugation) more than hepatocellular damage. A bilirubin rise together with markedly elevated ALT and AST points toward hepatocellular injury; alongside strongly raised ALP and GGT it points more toward bile-duct obstruction. A mildly elevated bilirubin without other abnormalities in an otherwise healthy person is almost always Gilbert's or a transient physiological variation from fasting or illness. Re-test after a normal eating pattern and adequate sleep to distinguish Gilbert's from a clinically relevant problem. Reference ranges are typically up to 17–20 µmol/L for total bilirubin, but this varies by laboratory — check your own lab's bound. A value above 50–70 µmol/L without a clear explanation warrants medical attention.

Educational information only — not medical advice. Consult a healthcare professional for clinical decisions.