Bilirubin
Bilirubin is formed from heme catabolism in the reticuloendothelial system.
Reference Ranges of Serum Bilirubin
In adult, the reference ranges of serum bilirubin are:
-Serum Total Bilirubin = 0.3-1 mg/dL (5.1-17 µmol/L)
-Serum Unconjugated (Indirect) Bilirubin = 0.2-0.7 mg/dL (3.4-12 µmol/L)
- Serum Conjugated (Direct) Bilirubin = 0.1-0.3 mg/dL (1.7 - 5.1 µmol/L)
However, in newborn, the reference ranges is usually higher than adult.
Hyperbilirubinemia
Hyperbilirubinemia exists when serum total bilirubin concentration
exceeds the upper limit of its reference range [1 mg/dL
(17µmol/L)] & when it reaches a certain concentration
(approximately 2.5-3 mg/dL); it diffuses into the tissues, which
then become yellow. This condition is called jaundice or
icterus.
Hyperbilirubinemia can be classified into:-
1- Pre-hepatic hyperbilirubinemia: Overproduction of bilirubin
above the capacity of the normal liver to metabolize it as in
hemolysis.
2- Hepatic hyperbilirubinemia: Failure of a damaged liver to
conjugate bilirubin produced in normal amounts.
3- Post-hepatic hyperbilirubinemia: Obstruction of the excretory
ducts of the liver that preventing the excretion of bilirubin.
Principle of Bilirubin Measurement:
Sulfanilic acid reacts with sodium nitrite to form diazotized sulfanilic acid.
In the presence of dimethyl sulfoxide, total bilirubin reacts with
diazotized sulfanilic acid to form azobilirubin that measured by
spectrophotometer.
In the absence of dimethylsulfoxide, only direct bilirubin reacts with
diazotized sulfanilic acid to form azobilirubin that measured by
spectrophotometer.
Indirect (unconjugated) bilirubin= Total bilirubin – Direct bilirubin