Bilirubin test: normal range and what the result means (BIL)

As ageing red blood cells break down, indirect (unconjugated) bilirubin is formed from haemoglobin. The liver joins it with glucuronic acid into direct (conjugated) bilirubin and excretes it in bile into the gut — which is why stools are brown. Total bilirubin is the sum of the two, and the ratio between them helps to find the cause: when most of it is indirect, the cause usually lies before the liver — too-fast breakdown of blood cells (haemolysis) or impaired conjugation in the liver (Gilbert syndrome — inherited, harmless, and per US population data found in about 3–7% of people, with bilirubin rising when fasting or ill). When direct bilirubin is raised, the cause is liver cell disease (hepatitis, cirrhosis) or an obstruction to bile flow (stones, a narrowed duct, a pancreatic or gallbladder tumour). Bilirubin is assessed together with ALT, AST, GGT and alkaline phosphatase.

• With jaundice — yellowed skin or whites of the eyes — this is the most common reason
• When liver or gallbladder disease is suspected: dark urine, pale stools, itching, pain on the right side under the ribs
• As part of liver tests, at a check-up or when monitoring liver disease
• When haemolytic anaemia is suspected
• In newborns — to monitor newborn jaundice

A raised bilirubin has three groups of causes: too-fast breakdown of blood cells (haemolytic anaemia, a reaction to a transfusion), liver diseases (hepatitis, cirrhosis, Gilbert syndrome) and obstructions to bile flow (stones, a narrowed duct, a pancreatic or gallbladder tumour). Which bilirubin is raised — direct or indirect — points to where to look. A small rise in the indirect fraction with no other changes is most often harmless Gilbert syndrome.

• Too-fast breakdown of red blood cells — haemolytic anaemia, a reaction to a blood transfusion, erythroblastosis of the newborn
• Liver diseases — hepatitis, cirrhosis
• Gilbert syndrome — an inherited, harmless disorder of conjugation
• A narrowing of the bile ducts
• Gallstones
• Pancreatic or gallbladder tumours

Symptoms that may go with a raised result

• Jaundice — yellowed skin and whites of the eyes
• Dark urine, pale stools
• Itching
• Tiredness, nausea
• Pain on the right side under the ribs

What to discuss with a doctor

• Direct and indirect bilirubin separately — their ratio shows where the cause lies
• ALT, AST, GGT, alkaline phosphatase — the picture of the liver and the bile ducts
• A full blood count and reticulocytes, if haemolysis is suspected
• An abdominal ultrasound scan, if an obstruction in the bile ducts is suspected
• Whether the symptoms and the bilirubin rise when fasting — a sign of Gilbert syndrome

Direct and indirect bilirubin

Indirect bilirubin is formed as blood cells break down and has not yet been processed by the liver; direct bilirubin has already been conjugated in the liver and is ready to be excreted in bile. When most of it is indirect, the cause is haemolysis or Gilbert syndrome; when the direct fraction is raised, it is liver disease or an obstruction to bile flow.

Gilbert syndrome

Gilbert syndrome is an inherited, harmless disorder in which the liver conjugates bilirubin more slowly. Indirect bilirubin tends to be slightly raised, especially when fasting, when ill or after stress, while the other liver markers are normal. No treatment is needed — MedlinePlus mentions it among the causes of a raised bilirubin. Per US population data it is found in about 3–7% of people.