Liver enzymes: what they do and how to test them

What are liver enzymes?

Measuring your liver enzymes is a useful way to check your liver health. There are 3 main liver enzymes:

• alkaline phosphatase (ALP) 
• alanine transferase (ALT) 
• gamma-glutamyl transpeptidase (GGT) 

What is alanine transferase (ALT)? 

Alanine transferase (ALT) is an enzyme found mainly in your liver. ALT is sometimes called alanine transaminase, alanine aminotransferase, or serum glutamic-pyruvic transaminase (SGPT). 

What is the function of ALT?

ALT helps break down proteins so your body can absorb them — so it’s important for your metabolism. 

What can cause your ALT levels to change?

Levels of ALT in the blood are normally quite low, as it’s mostly found in liver cells. So high ALT levels in your blood can be a sign of liver damage.

What are the most common symptoms?

High ALT levels often happen before symptoms of liver damage are obvious. So it's a good way to check for early signs of damage.

Some common symptoms for high ALT can include: 

• jaundice — yellow skin and eyes 
• itching
• nausea and vomiting 
• tiredness 
• unexplained weight loss
• swelling around your eyes, stomach, or legs

What is alkaline phosphatase (ALP)

Alkaline phosphatase (ALP) is an enzyme produced mainly by your liver. It’s also found in your bones, pancreas, and small intestine. An ALP blood test can help check that your liver and gallbladder are functioning properly.

What is the function of ALP?

Like ALT, ALP is important for your metabolism, as it helps break down proteins so your body can absorb them.

What can cause your ALP levels to change?

High ALP levels can be a sign of liver inflammation, damage to your gallbladder, or bone disease due to very low vitamin D levels. Low ALP levels are very rare but can be a sign that you’re not absorbing food properly — for example, if you have inflammatory bowel disease (IBD) or coeliac disease.

What are the most common symptoms of high ALP?

If your ALP levels are high as a result of liver damage, common symptoms include: 

• jaundice — yellow skin and eyes
• nausea and vomiting
• abdominal pain

High ALP might also indicate bone problems — symptoms might include bone pain and an increased risk of fractures.

What is gamma-glutamyl transpeptidase (GGT)

Gamma-glutamyl transpeptidase (GGT) is an enzyme found mainly in your liver, but also in your kidney, gallbladder, and pancreas. 

What is the function of GGT?

Like other liver enzymes, GGT also helps to break down protein. But its main function is moving other molecules around your body — playing a key role in helping your liver break down drugs and toxins.

What can cause your GGT levels to change?

High GGT levels can be a sign of liver damage or disease. If you drink too much alcohol, your GGT levels usually increase. Some drugs, including antibiotics and NSAIDs (nonsteroidal anti-inflammatory drugs) like ibuprofen, can also increase your levels.

What are the most common symptoms of high GGT?

If your GGT levels are high as a result of liver damage, common symptoms include: 

• jaundice — yellow skin and eyes 
• itching 
• nausea and vomiting
• tiredness
• unexplained weight loss 
• swelling around your eyes, stomach, or legs
  

How to test liver enzymes

You can test your liver enzymes with a liver blood test (previously known as a liver function blood test or LFT).

This test can’t formally diagnose or rule out any liver disease without further investigation from your GP or full medical context.

This means that the blood count for any of your liver enzymes measured might be normal even if you have liver disease. But an abnormal count can still occur in a normally functioning liver. 

A liver blood test might be helpful if you:

• have symptoms of fatigue and nausea
• have an eating disorder — like anorexia
• drink more than 14 units of alcohol a week
• are worried about fatty liver disease

When doing this blood test, one of our reporting GPs will review your:

• previous liver blood test results (if you have any)
• health profile 
• body mass index (BMI)
• alcohol consumption
• diet

These factors will give an understanding of how likely you are to develop liver disease .

What if you have abnormal liver enzyme results?

Mild to moderate abnormalities in liver enzymes are commonly associated with: 

• non-alcoholic fatty liver disease
• alcohol-related liver disease — for example, you might have elevated gamma-glutamyl transpeptidase (GGT) levels
• certain medication — like some antibiotics, anti-epileptic drugs, and non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, to name a few
• infections like hepatitis B and C

If your liver blood test results are abnormal, we recommend following them up with a healthcare professional. They will investigate your results further to help rule out or diagnose liver disease. 

The National Institute for Health and Care Excellence (NICE) recommend a FibroScan if you drink more than 50 units of alcohol a week for men, or 35 units or more a week for women. 

How to lower liver enzyme levels

A healthy lifestyle can help to lower raised liver enzymes levels caused by liver damage. This includes avoiding too much:

• saturated and trans fats — like fried foods, red meat, cakes, pastries, and cream 
• refined carbohydrates — like white bread and white pasta 
• added sugars — like fruit juices, fizzy drinks, and sweets 
• salt — like frozen foods, salted nuts, and smoked or cured meats 
• alcohol — limit to 14 units a week (equivalent to about 6 pints or 7 medium-sized glasses of wine)