Reference Range
Bilirubin is a tetrapyrrole and a breakdown product of heme catabolism. Most bilirubin (70%-90%) is derived from hemoglobin degradation and, to a lesser extent, from other hemo proteins. In the serum, bilirubin is usually measured as both direct bilirubin (DBil) and total-value bilirubin (TBil).
Direct bilirubin correlates with conjugated bilirubin but tends to overestimate actual conjugated bilirubin, as it includes both the conjugated bilirubin and bilirubin covalently bound to albumin (delta-bilirubin). Indirect bilirubin correlates with unconjugated bilirubin but tends to underestimate unconjugated bilirubin, as a portion of the unconjugated bilirubin reacts with diazosulfanilic acid, producing azobilirubin, which is measured as direct bilirubin.
Normal findings
Adult/elderly/child
:
Total bilirubin: 0.3-1.0 mg/dL or 5.1-17 μmol/L (SI units)
Indirect bilirubin: 0.2-0.8 mg/dL or 3.4-12.0 μmol/L (SI units)
Direct bilirubin: 0.1-0.3 mg/dL or 1.7-5.1 μmol/L (SI units)
Newborn
:
Total bilirubin: 1.0-12.0 mg/dL or 17.1-205 μmol/L (SI units)
Possible critical values
Total bilirubin
:
Adult: >12 mg/dL
Newborn: >15 mg/dL