Bilirubin – Understanding Your Blood Test Result

Section Editor: Christopher McCudden Ph.D., DABCC, FADLM, FCACB
September 23, 2026

Bilirubin is a yellow-orange pigment the body makes when it breaks down old red blood cells. The liver processes bilirubin and excretes it from the body in bile. It is measured as part of a liver panel and a comprehensive metabolic panel. On your report, it usually appears as a total bilirubin with a direct value beside it.

This article explains what the bilirubin test measures, and why the split between the direct and indirect fractions tells your doctor more than the total does. It also covers what a high result can mean, and why a mildly high bilirubin with normal liver enzymes is usually harmless.

The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal (or unexpectedly normal) result with your doctor.

What does the bilirubin test measure?

The bilirubin test measures how much bilirubin is circulating in your blood. Red blood cells live for about 120 days. When they are broken down, the hemoglobin inside them is taken apart, and bilirubin is one of the products.

At that point, bilirubin doesn’t dissolve in water, so it travels through the blood attached to a protein called albumin. This form is called unconjugated, or indirect, bilirubin. The liver takes it up and attaches a sugar to it, which makes it water-soluble. That form is called conjugated, or direct, bilirubin. The liver then sends it into bile, which drains through the bile ducts into the intestine, where it gives stool its brown color.

Why the direct and indirect fractions matter more than the total

A high total bilirubin tells your doctor that bilirubin is building up. It does not say where along the way the problem lies. The split between the two fractions does, because each one sits on a different side of the liver’s processing step.

Mostly indirect bilirubin. Bilirubin is arriving at the liver faster than it can be processed, or the processing step itself is running slowly. The problem is usually before the liver, or within the processing enzyme.
Mostly direct bilirubin. The liver has processed the bilirubin, but it cannot get out, or damaged liver cells are leaking it back into the blood. The problem is usually in the liver or in the bile ducts.

This is why a direct bilirubin is often added after a raised total comes back. The indirect value is rarely measured directly. It is calculated by subtracting the direct value from the total, so a report showing only the total and direct values contains everything your doctor needs.

How is the bilirubin test performed?

Bilirubin is measured on a routine blood sample, usually as part of a panel rather than on its own. A technologist collects blood from a vein, most often in your arm. You may be asked to fast beforehand, partly because fasting raises bilirubin slightly in some people.

The laboratory protects the sample from light because bilirubin breaks down when light reaches it, and an exposed sample can read falsely low. A difficult blood draw can also affect the result, since damaged red blood cells in the tube release their contents into the sample.

What do bilirubin results mean?

Your bilirubin result is read against the reference range printed on your own report, and alongside the liver enzymes measured at the same time. The figures below are typical for adults.

A normal total bilirubin. Most adults fall between approximately 0.2 and 1.2 mg/dL (3 to 21 µmol/L).
A normal direct bilirubin. This is usually below about 0.3 mg/dL (5 µmol/L), so most of the total is indirect.
A mildly high total with normal liver enzymes. This is a common finding. The excess is almost always indirect, and in most people it does not indicate liver disease.
A high bilirubin with abnormal liver enzymes. This combination points toward the liver or the bile ducts, and which enzymes are raised helps separate the two.
When jaundice becomes visible, the whites of the eyes usually turn yellow once total bilirubin passes roughly 3 mg/dL (51 µmol/L). Skin yellowing follows at higher levels.

What conditions and factors can affect bilirubin?

Bilirubin rises when more is produced than usual, when the liver cannot process it, or when processed bilirubin cannot drain away. The fraction that rises separates these situations.

Conditions and factors that mainly raise indirect bilirubin include:

Gilbert syndrome. An inherited reduction in the activity of the enzyme that processes bilirubin, present in an estimated 3 to 10 percent of people. Total bilirubin is usually below 3 mg/dL (51 µmol/L), liver enzymes are normal, and no treatment is needed or recommended.
Fasting, illness, and physical stress. In someone with Gilbert syndrome, bilirubin rises during these periods and settles afterward so that the result can look different from one test to the next.
Faster breakdown of red blood cells. Hemolytic anemia is the clearest example. A large bruise being reabsorbed can do the same thing for a short period.
Newborn jaundice. A rise in the first days of life is expected, because a newborn’s liver is still getting up to speed.
Certain medications. A few drugs slow the same processing step and raise indirect bilirubin without harming the liver.

Conditions and factors that mainly raise direct bilirubin include:

Injury to liver cells. Viral hepatitis, alcohol-related liver disease, and steatohepatitis all belong here, as does liver injury caused by a medication.
Blockage of the bile ducts. A gallstone in the duct is the most common cause. A narrowing, or a tumor of the bile duct or pancreas, can block the duct in the same way.
Damage to the smallest bile ducts inside the liver. Primary biliary cholangitis and primary sclerosing cholangitis are the main examples.
Long-standing liver scarring. In cirrhosis, bilirubin often rises late, once a large amount of liver tissue has been replaced by scar.

A bilirubin below the reference range is not considered a medical problem and is not investigated.

What other tests are ordered with bilirubin?

Bilirubin is interpreted alongside the other results on the same panel, and the pattern they form matters more than any single value.

The liver enzymes. ALT and AST rise mainly with injury to liver cells, while ALP and GGT rise mainly with blockage or irritation of the bile ducts.
A direct bilirubin. This is added when only a total was originally ordered, and the total came back high.
Albumin and INR. These show how well the liver is carrying out its manufacturing work, which bilirubin alone does not measure.
A complete blood count and a reticulocyte count. These are ordered when rapid breakdown of red blood cells may explain the jaundice.
An ultrasound of the liver and bile ducts. This is the usual first imaging test when a blockage is suspected.

What happens after a bilirubin test?

For mildly elevated total bilirubin with normal liver enzymes, the usual next step is to repeat the test. A direct bilirubin is added if it was not already reported. If the raised bilirubin is almost entirely indirect and everything else is normal, Gilbert syndrome is the most likely explanation, and it needs no treatment or monitoring.

If the direct fraction is raised, or if the liver enzymes are abnormal, your doctor will look for a cause. That usually means an ultrasound to check the bile ducts, along with blood tests for viral hepatitis and other liver conditions. A referral to a hepatologist or gastroenterologist follows if the cause is not clear or the results are marked.

Report symptoms regardless of the number shown. Yellowing of the eyes or skin and dark urine both need prompt attention. Also mention pale or clay-colored stools and persistent itching of the skin to your doctor.

Questions to ask your doctor

What was my total bilirubin, and what is the reference range at this laboratory?
Was a direct bilirubin measured, and how much of the total was direct?
Were my liver enzymes normal on the same test?
Could this be Gilbert syndrome, and does that need any follow-up?
Had I fasted, or been unwell, before this blood test?
Could any of my medications or supplements be raising my bilirubin?
Do I need an ultrasound or any other imaging?
Should this test be repeated, and when?
Has my bilirubin changed compared with previous blood tests?
What symptoms should prompt me to contact you before my next appointment?