Bilirubin is a yellowish pigment naturally produced in the body as red blood cells complete their life cycle and break down. This pigment travels through the bloodstream to the liver, where it undergoes chemical changes before being eliminated from the body. Measuring bilirubin levels is a common diagnostic tool that provides insights into liver function and red blood cell health.
Different Forms of Bilirubin
Bilirubin exists in two primary forms within the body: indirect, also known as unconjugated bilirubin, and direct, or conjugated bilirubin. Indirect bilirubin is initially formed when red blood cells break down in the bloodstream. This form of bilirubin is not water-soluble and travels through the blood attached to a protein called albumin.
Upon reaching the liver, indirect bilirubin undergoes a chemical process called conjugation. During this process, it combines with a sugar molecule, converting it into direct, or conjugated, bilirubin. Direct bilirubin is water-soluble, allowing it to be excreted by the liver into bile, which then moves into the intestines for elimination.
Steps for Calculating Indirect Bilirubin
Laboratories typically measure two specific bilirubin values from a blood sample: total bilirubin and direct bilirubin. Total bilirubin represents the sum of all bilirubin present in the blood, encompassing both indirect and direct forms. Direct bilirubin specifically measures the amount of bilirubin that has been processed by the liver.
To determine the amount of indirect bilirubin, a simple arithmetic calculation is performed. The quantity of direct bilirubin is subtracted from the total bilirubin measurement. The formula for this calculation is: Indirect Bilirubin = Total Bilirubin – Direct Bilirubin. For instance, if a blood test reveals a total bilirubin level of 1.2 milligrams per deciliter (mg/dL) and a direct bilirubin level of 0.3 mg/dL, the indirect bilirubin would be 0.9 mg/dL.
This calculation isolates the bilirubin that has not yet undergone processing in the liver. It provides a specific value for the unconjugated form, which is useful in assessing various bodily functions.
Meaning of the Calculated Value
The calculated indirect bilirubin level provides information about the initial stages of bilirubin processing in the body. An elevated level of indirect bilirubin can indicate that red blood cells are breaking down at an increased rate. This accelerated breakdown can occur due to various reasons, leading to a higher production of bilirubin than the liver can immediately process.
Alternatively, elevated indirect bilirubin might suggest that the liver is not effectively capturing or processing bilirubin as it arrives from the bloodstream. Its capacity to conjugate bilirubin could be temporarily overwhelmed or impaired. The calculated indirect bilirubin value is one piece of a larger diagnostic puzzle and should always be evaluated by a healthcare professional in conjunction with other clinical findings.