Bilirubin

You don’t need any special preparation for this test.

For adults and older children: A healthcare professional will take a blood sample from a vein in your arm. 

For newborn babies: A few drops of blood are usually collected from a heel prick. Sometimes bilirubin can be estimated by placing a device on the baby’s skin (transcutaneous bilirubin meter), though this may need to be followed up with a blood test. 

Important: Your blood sample might be protected from bright light before testing, as light can break down bilirubin. 

Bilirubin is not usually present in the urine, however a form of conjugated (direct) bilirubin is water-soluble and may be excreted into the urine when concentrations are high in the blood. This is usually tested via a urine dipstick test, as part of urinalysis. 

What the test measures 

Bilirubin is an orange-yellow pigment created when your body breaks down old red blood cells. Here’s how the process works: 

• Red blood cells normally live for about 120 days 
• When they break down, haemoglobin (the oxygen-carrying protein) is released 
• This haemoglobin is converted to unconjugated bilirubin (also called indirect bilirubin) 
• Your liver processes this unconjugated bilirubin by adding sugars to it, creating conjugated bilirubin (also called direct bilirubin) 
• The conjugated bilirubin is secreted into bile, which flows to your intestines 
• Bacteria in your intestines break it down further, eventually producing the brown pigment that colours normal stools 

Your body normally produces about 250 to 350 milligrams of bilirubin daily. Small amounts of unconjugated bilirubin are found in blood, but virtually no conjugated bilirubin should be present. 

The test usually measures total bilirubin. Sometimes your doctor may also request separate measurements of conjugated and unconjugated bilirubin (called a split bilirubin test) to help determine the cause of abnormal total bilirubin results. 

What your results mean 

When bilirubin levels rise too high, it causes jaundice (yellowing of the skin and whites of the eyes). Your doctor will need further tests to find out why. 

In adults and older children: 

High total or unconjugated bilirubin may indicate:  

• Haemolytic anaemia (excessive red blood cell breakdown) 
• Sickle cell anaemia 
• Pernicious anaemia 
• Blood transfusion reaction 

High conjugated bilirubin may indicate:  

• Blockage of the liver or bile ducts 
• Hepatitis 
• Liver trauma 
• Cirrhosis 
• Gallstones 
• Drug reaction 
• Long-term alcohol abuse 

In newborn babies: 

It is important to determine the age of the newborn baby when interpreting high bilirubin results. 

Physiological jaundice: It’s common for newborns to have slightly raised bilirubin between days 2 and 7 of life. This is called physiological jaundice. Up to 50% of full-term babies and even more premature babies develop this. The baby’s liver is not yet mature enough to process bilirubin quickly. This type of jaundice is not abnormal and usually resolves within a few days. 

Abnormal jaundice: Jaundice is concerning if it: 

• Occurs within the first 24 hours of life 
• Persists longer than 8–14 days 

Jaundice in the first 24 hours may be caused by haemolytic disease of the newborn, where the baby’s red blood cells are destroyed due to blood type incompatibility with the mother (haemolytic disease of the newborn). 

may be caused by abnormal liver metabolism or malformation of the bile ducts (biliary atresia). Biliary atresia requires early surgical treatment to avoid the need for liver transplantation. 

Important: Very high unconjugated bilirubin in newborns can damage developing brain cells (kernicterus), potentially causing mental impairment, hearing loss, speech difficulties, or seizures. When bilirubin gets too high, treatment includes phototherapy (exposing skin to blue light) and sometimes exchange blood transfusion. 

However, high bilirubin in older children and adults doesn’t pose the same risk to the brain, as the blood-brain barrier is more developed.

If your bilirubin is abnormal, your doctor will: 

• Review your other liver function test results 
• Consider your symptoms and medical history 
• May order additional tests to find the underlying cause 
• Develop a treatment plan based on the diagnosis 
• Monitor your condition over time 

Treatment depends entirely on what’s causing the elevated bilirubin. Your doctor will work with you to address the underlying problem.

Light exposure: 

Bright light can break down bilirubin, potentially giving falsely low results. Your sample might be protected from light before testing. 

Genetic conditions: 

Several inherited conditions can cause mildly raised bilirubin: 

• Gilbert syndrome (relatively common, affects up to 5% of people) 
• Dubin-Johnson syndrome 
• Rotor syndrome 
• Crigler-Najjar syndrome (rare and most serious, typically presents at birth) 

The first three are usually mild, long-term conditions that cause no significant health problems. Gilbert syndrome causes a small increase in bilirubin but no clinical issues other than occasional mild jaundice. Prolonged fasting or general illness can trigger mild jaundice in people with Gilbert syndrome. 

Bilirubin is usually measured as part of liver function tests, which may include: 

ALT (alanine aminotransferase): Measures liver cell damage 

AST (aspartate aminotransferase): Another marker of liver cell damage 

ALP (alkaline phosphatase): May indicate bile duct problems if raised alongside other LFT results. 

GGT (gamma-glutamyl transferase): Helps confirm liver or bile duct problems 

Albumin: Measures liver synthetic function 

Total protein: Overall protein levels in blood 

Additional tests that may be needed: 

• Urinalysis (bilirubin in urine indicates liver or bile duct blockage) 
• Hepatitis virus tests 
• Full blood count (to check for anaemia) 
• Imaging scans (ultrasound, CT, or MRI) 
• Liver biopsy (in some cases) 

Jaundice is the yellowing of skin and eyes caused by high bilirubin levels. It’s a symptom, not a disease itself, and requires investigation to find the underlying cause. 

For more information about jaundice and its causes, visit the NHS page on jaundice.