Direct (conjugated) bilirubin

Direct (conjugated) bilirubin is the form of bilirubin already processed by the liver and excreted in bile. Testing is performed when total bilirubin is elevated or in jaundice, because it helps distinguish a cause in the liver and bile ducts from increased red blood cell breakdown. Results are interpreted alongside total bilirubin and other liver tests.

Who is this test for

• people with elevated total bilirubin, to identify which form predominates;
• people with yellowing of the skin or whites of the eyes, dark urine, pale stools or itchy skin;
• people with suspected liver or bile duct disease, and for monitoring these diseases;
• infants with jaundice lasting longer than expected, as directed by a paediatrician.

What direct bilirubin is and what it shows

Bilirubin is formed through the breakdown of haemoglobin from ageing red blood cells. It travels to the liver bound to albumin as unconjugated (indirect) bilirubin. Liver cells combine it with glucuronic acid, forming conjugated bilirubin, which is water-soluble, is excreted through bile into the intestine and gives stools their brown colour.

A healthy person has very little direct bilirubin in the blood because the liver continually excretes it into bile. When it rises, bile excretion is impaired, either because of liver cell disease or obstruction in the bile ducts. Total bilirubin is the sum of both forms, while indirect bilirubin is calculated as the difference between total and direct bilirubin.

Preparation and sample

Blood is taken from a vein. Fasting is not essential for direct bilirubin, but if glucose, blood fats or prothrombin time are tested from the same draw, attend in the morning after fasting. Do not fast longer than a normal overnight fast, because prolonged fasting may temporarily raise bilirubin. State which medicines you take when your blood is drawn.

How results are interpreted

Bilirubin is expressed in micromoles per litre (µmol/L). Some international laboratories use mg/dL, and 1 mg/dL corresponds to approximately 17,1 µmol/L. The reference interval depends on the method; use the interval printed on your report. In adults, values up to about 5 µmol/L are most often considered normal, so even a small increase may be important.

If total bilirubin is slightly elevated and direct bilirubin is normal, the indirect form is elevated, most often because of harmless Gilbert’s syndrome.

Elevated direct bilirubin

Elevated direct bilirubin means the liver cannot excrete bile normally or bile flow is obstructed. The most common causes are:

• liver cell disease: viral or alcoholic hepatitis, drug-induced liver damage, cirrhosis;
• bile stasis within the liver (cholestasis): certain medicines and diseases of the intrahepatic bile ducts, such as primary biliary cholangitis;
• bile duct obstruction: gallstones, inflammation or narrowing of the bile ducts, tumours of the pancreas or bile ducts;
• rare inherited syndromes: Dubin-Johnson and Rotor syndromes, in which direct bilirubin is slightly elevated and liver enzymes are normal; they are harmless and require no treatment.

Other liver tests are usually abnormal alongside elevated direct bilirubin. When alkaline phosphatase and GGTpredominate, the cause is more likely in the bile ducts; when AST and ALT predominate, it is in liver cells. The next step is usually ultrasound, which shows whether the bile ducts are dilated (abdominal ultrasound is available only in Split). Once the cause is removed, for example after removing a stone, direct bilirubin sometimes returns to normal gradually over several weeks.

Types of jaundice: what blood, urine and stools show

Type of jaundice	Blood bilirubin	Urine	Stool
due to haemolysis or Gilbert’s syndrome	predominantly indirect, direct normal	no bilirubin	brown
hepatic (hepatitis, cirrhosis, medicines)	both forms elevated, often predominantly direct	dark, with bilirubin	brown or paler
due to bile duct obstruction	predominantly direct	dark, with bilirubin	pale, clay-coloured

The table shows typical patterns. In practice they overlap, so the doctor makes the final assessment using other results and an examination.

Direct bilirubin in a newborn

Ordinary neonatal jaundice comes from indirect bilirubin and usually resolves on its own. Elevated direct bilirubin in a newborn is not normal and requires prompt investigation, because it may indicate bile duct disease requiring early treatment. Contact a paediatrician if jaundice lasts longer than two weeks (three weeks in premature babies), or if stools are pale and urine is dark.

When to seek urgent medical attention

Jaundice with abdominal pain, fever or shaking chills requires urgent assessment because it may indicate bile duct inflammation. Also seek urgent help if you notice confusion, drowsiness, bleeding or vomiting blood alongside jaundice.

How to arrange testing

You can come for blood collection without an appointment or referral at one of our branches throughout Croatia (listed on the Contactpage). Prices for all tests and panels are listed in the service price list. Direct bilirubin is usually measured alongside total bilirubin, which is part of the Extended liver health panel.

Frequently asked questions

What is the difference between direct and indirect bilirubin?

Indirect bilirubin has not yet been processed by the liver and is most often elevated in Gilbert’s syndrome or increased red blood cell breakdown. Direct bilirubin has already been processed by the liver and rises when bile excretion is impaired by liver or bile duct disease.

Is elevated direct bilirubin a sign of Gilbert’s syndrome?

No. In Gilbert’s syndrome, indirect bilirubin is elevated, while direct bilirubin is generally normal. Elevated direct bilirubin requires another explanation.

What does slightly elevated direct bilirubin mean?

If other liver tests are normal and you have no symptoms, the doctor usually repeats the test. If alkaline phosphatase, GGT or liver enzymes also rise, or dark urine appears, further investigation follows, most often ultrasound.

Why is urine dark when direct bilirubin is elevated?

Direct bilirubin is water-soluble, so it passes into urine, making it dark like tea. Bilirubin in urine is detected by urine dipstick examination.