A bilirubin test assesses the quantity of bilirubin in the bloodstream by measuring the content within a blood sample.

Bilirubin is a byproduct of red blood cell destruction and exists in a free form (unconjugated or indirect biliruin) until it is taken up by liver cells. Here it is converted into a soluble form (conjugated or direct bilirubin) by binding with glucuronic acid which is catalyzed by the enzyme glucuronyl transferase. It is then passed out with bile into the gut and eventually expelled with the stool.

For more information on bilirubin in the liver, blood and urine, refer to the article on What is Bilirubin?

A complete bilirubin test will indicate the total bilirubin (direct + indirect) and direct bilirubin. From these two results, the indirect bilirubin levels can be calculated.

Depending on regional differences in values and testing methodology in the laboratory, the results may be expressed as mg/dL or mmol/L.

Bilirubin Test Results, Values and Readings

The reference range may vary among laboratories. Bilirubin levels higher or lower than the normal values may not require immediate treatment unless it is persistent and reaches levels which are dangerously high.

Adults

  • Total Bilirubin
    • mg/dL Normal (Reference Range) = 0.3 to 1.0 mg/dL
    • mmol/L Normal (Reference Range) = 5.1 to 17 mmol/L
  • Direct Bilirubin (Conjugated)
    • mg/dL Normal (Reference Range) = 0.1 to 0.3 mg/dL
    • mmol/L Normal (Reference Range) = 1.7 to 5.1 mmol/L
  • Indirect Bilirubin (Unconjugated)
    • mg/dL Normal (Reference Range) = 0.2 to 0.8 mg/dL
    • mmol/L Normal (Reference Range) = 3.4 to 12.0 mmol/L

Elevated bilirubin levels in the blood (hyperbilirubinemia) will result in jaundice. Different types of jaundice indicates whether the causative disorder lies before bilirubin enters the liver cells (pre-hepatic), within the liver cells (hepatocellular) or after it leaves the liver cells (obstructive jaundice).

Newborns (Infants)

  • Full-Term Baby
    • 1 day old (less than 24 hours) = Less than 6.0 mg/dL or 103 mmol/L
    • 2 day old (less than 48 hours) = Less than 10.0 mg/dL or 170 mmol/L
    • 3 to 5 days = Less than 12.0 mg/dL or 205 mmol/L
    • 7 days or older = Less than 10.0 mg/dL or 170 mmol/L
  • Premature Baby
    • 1 day old (less than 24 hours) = Less than 8.0 mg/dL or 137 mmol/L
    • 2 day old (less than 48 hours) = Less than 12.0 mg/dL or 205 mmol/L
    • 3 to 5 days = Less than 15.0 mg/dL or 256 mmol/L
    • 7 days or older = Less than 15.0 mg/dL or 256 mmol/L

Neonatal jaundice (jaundice in newborns) is not uncommon. The immature liver coupled with rapid destruction of unneeded red blood cells after birth causes an elevation of bilirubin levels in most newborn babies. However, this may not always lead to visible yellow discoloration of the skin and eyes as would be expected in jaundice.

Apart from physiologic jaundice, breastfeeding and breast milk jaundice are other non-pathological causes of jaundice in newborns. Treatment will depend on the cause of the jaundice and bilirubin levels.

Related Articles

  1. What is Jaundice?
  2. Types of Jaundice
  3. Jaundice in Newborns

References

  1. Bilirubin. University of Michigan

Article reviewed by Dr. Greg. Last updated on April 12, 2011