Liver function tests

What are liver function tests?

Liver function tests, sometimes called a liver panel or LFTs, are a group of blood tests that measure different substances made by your liver. Together, they give your doctor information about how well your liver is working and whether it might be damaged or inflamed.

Why might I need one?

Your doctor may request liver function tests if you have symptoms that could suggest a liver problem, such as:

• jaundice (yellowing of the skin and eyes)
• dark urine or pale stools
• nausea, vomiting or loss of appetite
• swelling or pain in your abdomen
• unusual tiredness or itching.

You may also be tested even without symptoms, since liver disease can develop silently for years. Sources suggest that around 15 to 20% of adults have an abnormal result on liver blood tests, often found during a routine check-up rather than because of symptoms.

You might be offered testing if you:

• drink alcohol regularly, or have a family history of liver disease
• are living with obesity, type 2 diabetes, or a raised body mass index or waist size
• have had a scan showing fatty changes in your liver
• have been exposed to a hepatitis virus, inject drugs, have older tattoos done before strict infection control, or have moved from an area with high hepatitis rates
• take a long-term medicine that can affect the liver, either before starting it or to monitor it while you're taking it.

If you already have a diagnosed liver condition, these tests can also be used to monitor how it's progressing, or how well your treatment is working.

What are the benefits of having it?

Liver function tests are quick and simple, needing only a small blood sample, so they're an easy way to check on your liver as part of a routine health check.

Because liver disease often causes no symptoms until it's fairly advanced, catching problems early through testing gives you the best chance to make lifestyle changes, get vaccinated, or start treatment before more serious damage develops.

Are there different types of the test?

Liver function tests aren't a single test, but a panel of several blood tests done on one sample. The specific tests can vary, but commonly include the following:

• Alanine aminotransferase (ALT) and aspartate aminotransferase (AST): These are enzymes that rise when liver cells are damaged or inflamed
• Alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT): These can point to a problem with your bile ducts
• Bilirubin: A substance that builds up if your liver isn't clearing it properly, causing jaundice (yellowing of the skin and eyes)
• Albumin and total protein: These show how well your liver is making protein.

How do I prepare for the test?

Follow whatever instructions you're given for your specific appointment. There’s a chance you may need to fast for 10 to 12 hours beforehand.

Tell your doctor about all medications, supplements and herbal products you're taking, including over-the-counter painkillers, since these can affect your results. Don't stop taking anything unless your doctor tells you to.

What happens during the test?

1. A healthcare professional finds a vein in your arm, usually inside your elbow crease, and cleans the area
2. They may wrap a band around your arm to make the vein easier to find
3. A small needle is inserted into the vein, and a small amount of blood is drawn into a tube or vial
4. You may feel a brief sting as the needle goes in or comes out
5. The needle is removed and a small dressing or plaster is applied.

The test itself usually takes less than 5 minutes.

What happens after the test?

As long as you're not feeling lightheaded from the blood draw, you can go home straight away, and you can eat, drink and take your usual medications again.

Your blood sample is sent to a laboratory, and results can take anywhere from a few hours to a few weeks, depending on where you're tested.

An abnormal result doesn't automatically mean you have liver disease. Many other things, including some medicines, alcohol, recent illness, exercise, or pregnancy, can affect these tests, and mild changes are often temporary. Your doctor will look at the overall pattern of your results, alongside your symptoms and medical history, and may repeat the test to check if things have settled.

Equally, a normal result doesn't completely rule out liver disease, since your liver can often keep working normally even with some damage. If your doctor still has concerns, they may suggest further tests, such as a scan or a liver biopsy.

What are the risks or side effects?

Liver function tests carry very little risk, since they only involve a standard blood test. You might have brief pain or slight bruising where the needle was inserted, and this usually settles quickly. Some people feel a little lightheaded during or after a blood draw.