Bilirubin Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Bilirubin?

Bilirubin is a yellow-orange pigment produced when red blood cells reach the end of their lifespan (approximately 120 days) and are broken down. The haemoglobin released is converted first to biliverdin and then to unconjugated (indirect) bilirubin. This unconjugated bilirubin travels to the liver, where it is conjugated (made water-soluble) and excreted into bile. It is bilirubin that gives bile its characteristic colour, and when it accumulates in the skin and eyes, it causes jaundice.

A bilirubin blood test typically measures total bilirubin (the sum of all forms), but can be broken down into direct (conjugated) and indirect (unconjugated) fractions. This breakdown is clinically important because it helps distinguish between different causes of jaundice - pre-hepatic (excess red cell breakdown), hepatic (liver disease), and post-hepatic (bile duct obstruction).

Why Is Bilirubin Tested?

• Investigate jaundice - yellowing of the skin and whites of the eyes
• Assess liver function as part of a liver function test (LFT) panel
• Diagnose and differentiate types of liver disease (hepatitis, cirrhosis, drug reactions)
• Detect bile duct obstruction (gallstones, tumours, strictures)
• Investigate haemolytic anaemia (excessive red blood cell destruction)
• Monitor patients on hepatotoxic medications
• Diagnose Gilbert syndrome - a common benign condition causing intermittent mild jaundice

Normal Ranges

Jaundice typically becomes visible when total bilirubin exceeds 35–40 µmol/L. In Gilbert syndrome, total bilirubin is usually 21–70 µmol/L and predominantly unconjugated.

Causes of High Bilirubin

Predominantly Unconjugated (Indirect)

• Gilbert syndrome: Affects 5–10% of the population - benign, intermittent, and often discovered incidentally
• Haemolytic anaemia: Sickle cell disease, thalassaemia, autoimmune haemolysis, or transfusion reactions
• Ineffective erythropoiesis: B12 or folate deficiency causing premature red cell destruction
• Large haematoma reabsorption: After trauma or surgery
• Neonatal jaundice: Common in newborns due to immature liver conjugation

Predominantly Conjugated (Direct)

• Bile duct obstruction: Gallstones, pancreatic head tumour, cholangiocarcinoma
• Hepatitis: Viral (A, B, C, E), alcoholic, autoimmune, or drug-induced
• Cirrhosis: End-stage liver disease from any cause
• Drug-induced liver injury: Paracetamol overdose, antibiotics, statins, herbal remedies
• Primary biliary cholangitis: Autoimmune destruction of intrahepatic bile ducts

Causes of Low Bilirubin

Low bilirubin is not usually clinically significant. Very low levels may be seen with:

• Some medications (phenobarbital, caffeine)
• Exposure to UV light (phototherapy in neonates)

How to Support Healthy Bilirubin Levels

• Protect your liver: Limit alcohol, avoid paracetamol overuse, and maintain a healthy weight
• Stay hydrated: Good hydration supports liver and kidney function
• Eat a liver-friendly diet: Cruciferous vegetables, leafy greens, and antioxidant-rich foods support liver detoxification
• Manage Gilbert syndrome: If diagnosed, no treatment is needed - mild jaundice may worsen with fasting, illness, or stress but is harmless
• Review medications: Discuss any hepatotoxic medications with your GP
• Get vaccinated: Hepatitis A and B vaccines protect against viral causes of elevated bilirubin

When Should You Get Tested?

• You notice yellowing of your skin or the whites of your eyes
• You have dark urine (tea-coloured) or pale stools
• You experience abdominal pain, particularly in the upper right area
• You are taking medications known to affect the liver
• You have a history of liver disease or gallstones
• You have unexplained fatigue, itching, or nausea

Which Lola Health Tests Include Bilirubin?

• Peak Insights - includes full liver function panel with total and direct bilirubin
• Vital Check — includes liver function tests with bilirubin
• Core Health — essential health screening including bilirubin