What is bilirubin?

Ever wondered why bruises turn yellow? Find out about bilirubin and what it can tell you about your health.

Bilirubin. It’s why skin turns yellow with jaundice and what makes our stools brown. Your bilirubin levels say a lot about your health and can be dangerous if your levels are too high. 

In this article, we cover:

What is bilirubin?

Bilirubin is a yellow-brown pigment found in bile. Bile helps to 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 normal process of breaking down old red blood cells. This means it is a waste product.

How is bilirubin excreted?

Bilirubin is carried to the liver by albumin, a simple protein. Here, the bilirubin becomes conjugated. This means it is now water-soluble and can be eliminated from the body. It is stored in the gall bladder 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 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 follow up with a urine test, other 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 will vary slightly between laboratories. 

Jaundice (yellowing of the skin and eyes) becomes visible when the bilirubin level is 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 hyperbilirubinaemia. Some of the most common causes are gallstones, alcoholic liver disease, and hepatitis. But there are many other different 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. This is usually 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 disorders — This may include conditions like lupus, rheumatoid arthritis, or ulcerative colitis.
  • Medications — Antibiotics like ceftriaxone can occasionally cause red blood cells to break down. 
  • Blood cancers
  • Mechanical heart valves

Within the liver

If the liver is not 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 non-alcohol fatty liver disease — Both alcohol and being overweight can cause 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 increase because it is unable to 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 related to problems with the liver.

You can improve or maintain your liver health by: 

  • Cutting down alcohol — Avoid exceeding 14 units per week. It’s best to drink as little as possible.
  • 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 increases your risk of hepatitis B and C. 
  • Following medication instructions — Certain medicines can harm your liver. Always check the label before taking and don’t take over 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?

Consult your doctor if your bilirubin levels are significantly raised or you’ve developed jaundice. Depending on your levels, they may wish to request further tests, like an ultrasound or another blood test, especially if the cause is not immediately obvious. 


  1. North Bristol NHS Trust. n.d. Bilirubin. [online] Available at: <https://www.nbt.nhs.uk/severn-pathology/requesting/test-information/bilirubin> [Accessed 7 April 2022].

Related tests

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