Definition
cBilirubin is the total concentration of bilirubin in plasma. The systematic symbol for arterial blood is cBilirubin(aP). The analyzer symbol may be ctBil.
What does cBilirubin tell you
Bilirubin is formed as a result of the catabolism of hemoglobin. Typically, the major part of bilirubin in plasma comes from the breakdown of red cells. Most of the initially produced unconjugated bilirubin is in plasma reversibly bound to albumin, but the unbound part is toxic.
In children and adults, bilirubin is conjugated in the hepatocytes to water-soluble, non-toxic conjugated bilirubin, which is excreted in the bile. Neonates have an increased breakdown of hemoglobin, a limited hepatic function, and low concentrations of albumin. In neonates with jaundice, the concentration of free unconjugated bilirubin is therefore relatively high with risk of neurotoxicity (kernicterus).
If the concentration of bilirubin in neonates exceeds defined levels, it requires specific therapy (see below). If cBilirubin exceeds 30-40 µmol/L, it causes a yellow-coloring of the skin, i.e., jaundice.
Reference ranges
< 24 hours, premature, 17-137 µmol/L (1-8 mg/dL)
< 24 hours, full-term, 34-103 µmol/L (2-6 mg/dL)
< 48 hours, premature, 103-205 µmol/L (6-12 mg/dL)
< 48 hours, full-term, 103-171 µmol/L (6-10 mg/dL)
3-5 days, premature, 171-239 µmol/L (10-14 mg/dL)
> 1 month, 3.4-17 µmol/L (0.2-1.0 mg/dL)
disclaimer
Clinical interpretation
Hyperbilirubinemia is due to increased production, decreased elimination, or a combination of both.
A. Increased production:
Hemolysis
Common causes:
- Infection
- Chemical-toxical reaction
- Immunization (auto-immune disease or iso-immunization)
- Hereditary disease
B. Decreased elimination:
Intrahepatic cholestasis
Common causes:
- Viral infection (hepatitis of any kind)
- Primary biliary cirrhosis
- Toxic reactions (medicaments)
Extrahepatic cholestasis
Common causes:
- Gallstones
- Cholecystitis
- Cancer
- Biliary atresia
Considerations
In children and adults, jaundice will, in almost all cases, be due to conjugated bilirubin. The hyperbilirubinemia itself is only a symptom, and the treatment will be directed towards the cause of the hyperbilirubinemia. In newborns, hyperbilirubinemia is typically caused by unconjugated bilirubin and, therefore, requires specific treatment.
The treatment modalities are:
- Phototherapy
- Exchange transfusion
The concentration of bilirubin indicating treatment varies depending on the gestational age and weight, as well as on the general condition of the baby. The more premature and the more ill the baby, the lower the action limit for therapy.
Several diseases in the newborn, i.e., immunization, infection, hypothyroidism, biliary atresia, and galactosemia, may cause hyperbilirubinemia, and although in most cases this is simple hyperbilirubinemia, the clinician has to be aware of underlying disease. Signs of such are high cBilirubin in cord blood, early (< 24 hrs.) hyperbilirubinemia, steep increase in cBilirubin, and prolonged hyperbilirubinemia.
