Bilirubin is the product of red blood cell breakdown.
The bilirubin initially is "unconjugated", and travels through the bloodstream to the liver. In the liver, it is metabolized to "conjugated" bilirubin, and excreted in the liver bile.
An increase in breakdown of red cells (such as in hemolysis) leads to an increase in unconjugated bilirubin. Liver disease leads to loss of conjugated bilirubin into the bloodstream and a measurable increase.
Total bilirubin is a combination of both conjugated and unconjugated bilirubin.
Elevations in unconjugated bilirubin are found in:
Hemolysis
Trauma leading to a hematoma
Hemorrhagic pulmonary infarcts
Elevations in conjugated bilirubin are found in:
Pancreatic cancer
Obstruction of the bile duct
Elevations in both unconjugated and conjugated bilirubin are found in:
Hepatitis
Cirrhosis
Liver cancer
Drug-induced cholestasis
Normal Values*
Total
0.2–1.0 mg/dL
3–17 µmol/L
Unconjugated ("indirect")
0.2–0.8 mg/dL
3–13 µmol/L
Conjugated ("direct")
0–0.2 mg/dL
0–4 µmol/L
*These are general values taken from a variety of sources. The actual normal values may vary from lab to lab and from one type of testing protocol to another.
Source: Operational Medicine 2001, Health Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington DC, 20372-5300
