What is an Indirect Bilirubin Test?
An indirect bilirubin test measures the amount of indirect (unconjugated) bilirubin in your blood.
Bilirubin is a yellow substance produced when your body breaks down old or damaged red blood cells. The initial form of bilirubin is called unconjugated or indirect bilirubin.
Indirect bilirubin is not water-soluble, so it travels through the bloodstream attached to a protein called albumin. When it reaches the liver, the liver processes it and converts it into direct (conjugated) bilirubin, which can then be excreted through bile.
Measuring indirect bilirubin can help evaluate conditions involving red blood cell breakdown, bilirubin production, or the liver's ability to process bilirubin.
Other names: Unconjugated bilirubin, Indirect bilirubin, IBIL.
What is the Indirect Bilirubin Test Used For?
An indirect bilirubin test may be used to help:
Investigate jaundice (yellowing of the skin or eyes).
Evaluate possible hemolysis (increased breakdown of red blood cells).
Investigate suspected hemolytic anemia.
Help distinguish between different causes of elevated bilirubin.
Evaluate disorders affecting the liver's ability to process bilirubin.
Help diagnose certain inherited bilirubin disorders, such as Gilbert syndrome.
Evaluate bilirubin levels in newborns.
Monitor certain liver and blood disorders.
Indirect bilirubin is usually interpreted together with total bilirubin and direct bilirubin, as well as other laboratory tests.
Why Might I Need an Indirect Bilirubin Test?
Your healthcare provider may recommend this test if you:
Have yellowing of the skin or whites of the eyes.
Have unexplained elevation of total bilirubin.
Have symptoms or laboratory findings suggesting increased red blood cell destruction.
Have anemia with an unclear cause.
Have suspected hemolysis.
Have suspected Gilbert syndrome or another inherited bilirubin disorder.
Are being evaluated for liver or blood disorders.
Need evaluation of elevated bilirubin as part of a newborn assessment.
What Happens During an Indirect Bilirubin Test?
The test is usually performed using a blood sample.
A healthcare professional will collect a small amount of blood from a vein in your arm using a small needle. The procedure generally takes only a few minutes.
You may feel a brief sting when the needle is inserted or removed. Mild bruising or tenderness may occur at the collection site.
Will I Need to Do Anything to Prepare for the Test?
Usually, no special preparation is required for an indirect bilirubin test.
However, if the test is ordered together with other blood tests, your healthcare provider or laboratory may provide additional preparation instructions.
Follow the instructions provided by your healthcare provider or laboratory.
Are There Any Risks to the Test?
There is very little risk associated with a blood test.
You may experience slight pain, bruising, or tenderness where the blood was collected. These effects usually disappear quickly.
What Do the Results Mean?
Indirect bilirubin is generally interpreted together with total bilirubin, direct bilirubin, liver enzymes, complete blood count (CBC), and other tests when appropriate.
Indirect Bilirubin Level Possible Interpretation
Normal Generally indicates a normal level of unconjugated bilirubin
High May indicate increased red blood cell breakdown or reduced bilirubin processing by the liver
Low Usually not considered clinically significant
High Indirect Bilirubin
An elevated indirect bilirubin level may occur when the body is producing more bilirubin than the liver can process or when the liver has difficulty converting unconjugated bilirubin into its conjugated form.
Possible causes include:
Hemolysis or increased red blood cell destruction
Hemolytic anemia
Large hematoma or internal bleeding being broken down
Gilbert syndrome
Certain inherited disorders affecting bilirubin conjugation
Newborn jaundice
Reduced bilirubin conjugation in some liver conditions
Certain medications or medical conditions affecting bilirubin metabolism
Indirect Bilirubin and Hemolysis
When hemolysis is suspected, indirect bilirubin is usually evaluated together with other laboratory findings, such as:
Hemoglobin
Reticulocyte count
LDH
Haptoglobin
Peripheral blood smear
A pattern of increased indirect bilirubin + increased LDH + decreased haptoglobin + increased reticulocytes can support the possibility of hemolysis, although results must be interpreted in the clinical context.
Direct vs. Indirect Bilirubin
Bilirubin is commonly divided into two forms:
Indirect (unconjugated) bilirubin:
The form produced from the breakdown of heme. It is not water-soluble and circulates in the blood bound to albumin. Increased levels may occur with hemolysis or impaired bilirubin conjugation.
Direct (conjugated) bilirubin:
The form processed by the liver and made water-soluble. Increased levels may occur when bilirubin excretion is impaired or bile flow is obstructed.
Indirect bilirubin can commonly be calculated from total and direct bilirubin:
Indirect bilirubin = Total bilirubin − Direct bilirubin
Important Note
An elevated indirect bilirubin level does not by itself establish the cause.
The result should be interpreted together with total and direct bilirubin, CBC, reticulocyte count, LDH, haptoglobin, liver enzymes, medical history, and clinical findings, when appropriate.
Reference ranges may vary between laboratories, testing methods, age groups, and patient populations. Always interpret the result using the reference interval provided on the laboratory report.
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