Thursday, March 28, 2024

Bilirubin

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

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