What is bilirubin?

Bilirubin. It’s why skin turns yellow with jaundice and what makes our stools brown. Your bilirubin levels can tell you a lot about your health, and if they get too high, it could be a sign of something more serious.

In this article, we cover:

• What is bilirubin?
• Why do I need a bilirubin test?
• What is a normal bilirubin level?
• What causes increased bilirubin levels?
• How to lower bilirubin
• What should I do if my bilirubin result is abnormal?

What is bilirubin?
 

Bilirubin is a yellow-brown pigment found in bile. Bile helps your body digest food by breaking down fats into fatty acids and absorbing fat-soluble vitamins. 
 

How is bilirubin produced?
 

Most bilirubin comes from the body’s natural breakdown of old red blood cells. It’s a waste product.
 

How is bilirubin excreted?
 

Bilirubin is carried to the liver by a protein called albumin. In the liver, it becomes conjugated, which means it becomes water-soluble so it can be removed from the body. It’s then stored in the gallbladder and released into the gut. Most of it comes out in the faeces, but some is reabsorbed into the bloodstream back to the liver or filtered through the kidneys into the urine. 
 

Why do I need a bilirubin test?
 

Your doctor may request a bilirubin blood test if they suspect you have liver damage or liver disease.

Symptoms of liver disease can include: 

• Yellowish skin or whites of the eyes (jaundice)
• Abdominal pain
• Dark urine
• Pale stools
• Flu-like symptoms, such as fever and chills

You may also have your bilirubin level checked regularly if you are being treated for liver disease. 

Bilirubin is rarely tested on its own. Bilirubin forms part of a liver function test, which usually also includes alkaline phosphatase (ALP), gamma GT (GGT), and alanine transferase (ALT). If your results are abnormal, your doctor may suggest a urine test, further blood tests, or an ultrasound scan.
 

What is a normal bilirubin level?
 

A normal bilirubin level for adults is generally less than 21µmol/L or 1.2 mg/dl [1]. Reference ranges can vary slightly between laboratories. 

Jaundice (yellowing of the skin and eyes) becomes visible when the bilirubin level reach about 34 to 51µmol/L or 2 to 3 mg/dl. 

You can check your bilirubin levels with our at-home Liver Blood Test. 
 

What causes increased bilirubin levels?
 

A high level of bilirubin in the blood is known as Hyperbilirubinemia. Some of the most common causes are gallstones, alcoholic liver disease, and hepatitis. But there are many other reasons why bilirubin may be raised.

Problems can occur at different points during bilirubin’s life cycle, resulting in raised levels. 
 

Before reaching the liver

Some conditions cause bilirubin levels to rise before it reaches the liver, often due to increased red blood cell destruction. This can be caused by: 

• Sickle cell disease or thalassaemia — These inherited conditions produce red blood cells that don’t live as long as normal red blood cells.
• Autoimmune haemolytic anaemia — The immune system destroys red blood cells prematurely, increasing bilirubin production.
• Medications — Antibiotics like ceftriaxone can occasionally cause red blood cells to break down.
• Some haematological malignancies — Certain blood cancers can cause haemolysis or increased red-cell turnover.
• Mechanical heart valves
• Within the liver

If the liver isn’t working properly, it may be unable to process bilirubin and make it water-soluble for excretion. For example: 

• Viral hepatitis— This may be caused by viruses like hepatitis A, B, C, D, or E.
• Alcoholic liver disease and metabolic dysfunction- associated steatotic liver disease (MASLD) (formerly known as non-alcoholic fatty liver disease (NAFLD)) — Alcohol and metabolic dysfunction leading to fatty liver/ MASLD can lead to long-term liver damage.
• Cirrhosis— Cirrhosis is a late stage of liver scarring caused by long-term liver damage.
• Gilbert’s syndrome— Gilbert’s syndrome is genetic condition that can cause mild and occasional episodes of jaundice, usually linked to physical or mental stress.
• Paracetamol overdose
• Autoimmune hepatitis — This is where the immune system attacks the liver cells.
• Liver cancer
   

After leaving the liver

Once bilirubin has left the liver, levels may rise because it can’t leave the body, usually due to a blockage. This may be due to: 

• Gallstones
• Pancreatitis — This is where the pancreas becomes inflamed, often due to gallstones or alcohol abuse.
• Tumours — Tumours can compress the bile duct causing a blockage.
• Bile duct strictures — This is where there is a narrowing of the bile duct.

How to lower bilirubin
 

As with most abnormal blood test results, the best way to improve your bilirubin levels is to treat the underlying cause. Most causes are linked to liver health.

You can improve or maintain your liver health by: 

• Cutting down on alcohol — Avoid exceeding 14 units per week, and the less you drink, the better.
• Maintaining a healthy weight and exercising regularly — Being overweight can lead to fatty liver disease, causing inflammation.
• Practising safe sex — Unprotected sex with new partners can increase your risk of hepatitis B and C.
• Following medication instructions — Some medicines can harm your liver. Always check the label and don’t take more than the recommended dose. 

For more advice, visit our blog: 7 ways to keep your liver healthy. 

What should I do if my bilirubin result is abnormal?
 

You should speak to your doctor if your bilirubin levels are significantly raised or you’ve developed jaundice. Depending on your levels, they may want to arrange further tests, such as an ultrasound or another blood test, especially if the cause isn’t immediately clear. 

References

1. North Bristol NHS Trust. n.d. Bilirubin. [online] [Accessed: 12 August, 2026].