How do I Calculate the Indirect Bilirubin?

Bilirubin tests are performed on blood drawn by venipuncture or heelstick.

Bilirubin is formed from the breakdown of hemoglobin in red blood cells. A water-insoluble form of bilirubin called non-conjugated or indirect bilirubin (BU) circulates in the blood or finds its way to the liver where it is conjugated by the addition of sugars to the molecule. This water-soluble form, called direct bilirubin (BC), travels in the bile to the gallbladder for storage or straight to the small intestine. Doctors order bilirubin tests to diagnose certain liver and gallbladder disorders.

Things You'll Need

• Total Bilirubin results
• Direct Bilirubin results

Instructions

1. Collect a blood sample either through venipuncture in adults or a heelstick puncture from infants. (Alternatively, a non-invasive transcutaneous bilirubin meter can be placed against the skin to measure bilirubin.) Make sure the patient hasn't had anything to eat or drink for four hours prior to giving blood.

2. Centrifuge the sample separating the blood cells from the serum. Send the serum to a laboratory technician for a chemical analysis to measure the bilirubin levels.

3. Calculate the indirect bilirubin from the lab results. Subtract the direct bilirubin from the total bilirubin to find the indirect bilirubin: TBIL - BC = BU.

Tips & Warnings

• New technology is making it possible to measure non-conjugated bilirubin directly, precluding the need to calculate BU in the traditional fashion described here.

References

• WebMD: Digestive Disorders-Bilirubin
• Lab Tests Online: Bilirubin
• Medline Plus: Bilirubin - Blood

Resources

• Read this Article in Spanish