Jaundice will be apparent when the serum bilirubin is three times above normal. The normal value of bilirubin is <17 micromol/L.

A urinalysis will be useful in the initial stages of differentiating the causes of jaundice. It will also guide further investigations.

Pre-hepatic hyperbilirubinaemia

Unconjugated bilirubin is bound to albumin and is not water soluble. Therefore, it cannot appear in the urine.

Post-hepatic hyperbilirubinaemia

Conjugated bilirubin is water soluble and therefore appears in the urine. Urobilinogen is absent due the inability of conjugated bilirubin to be excreted in to the small intestine.

Pre-hepatic hyperbilirubinaemia No bilirubin Urobilinogen ++
Hepatic hyperbilirubinaemia Bilirubin + Urobilinogen ++
Post-hepatic hyperbilirubinaemia Bilirubin ++ No Urobilinogen

Urinalysis findings

The findings in the urine should then be confirmed by measuring direct (conjugated) and total bilirubin levels:

Urine is negative for bilirubin

Urine is positive for bilirubin