What is a liver function test, how to test it & what does it show?

The liver is the largest internal organ and performs many essential tasks. The liver plays a vital role in digestion by making bile to absorb fats, and it filters the blood from the digestive system breaking down fats, carbohydrates and proteins. In addition, the liver detoxifies chemicals in the blood stream, metabolises many drugs, makes proteins important for blood clotting and removes waste products through excretion in bile. A liver function test looks for damage to this organ which may arise from a wide variety of conditions including obesity, infections, and alcohol misuse.

In this article you can find out exactly what a liver function test is, what it shows and what the results mean.

What is a liver function test?

A liver function test (LFT) is a blood test used to diagnose and monitor damage to the liver. The test looks at the level of a number of enzymes and proteins that are produced by the liver.

A liver function test involves drawing a small sample of blood from a person’s inner arm with a needle and analysing the blood in a laboratory. The process of taking the blood is commonly done a nurse or phlebotomist, and is quick and usually causes only minor discomfort for a short period of time. A blood sample can also be taken with a simple finger prick, which is generally an option taken by those who would prefer to take their own sample from the comfort of their own home.

As the liver performs numerous vital bodily functions, problems can result in significant illness and can even be life-threatening. Detecting hidden issues and treating problems early may prevent serious complications later. Many liver disorders are initially symptomless though they may cause a wide variety of symptoms such as weakness, unexplained weight loss, fatigue, ascites (fluid collection in the abdomen), discoloured urine or stools, and abnormal bruising or bleeding.

What does a liver function test show?

A liver function test will measure the levels of the certain enzymes and proteins in the bloodstream such as:

  • ALT (Alanine Aminotransaminase) is an enzyme found principally in the liver. Its role is to help convert proteins into energy for the liver cells. ALT levels are normally low but when the liver is damaged, it releases more ALT into the blood, causing the level to rise.
  • AST (Aspartate aminotransferase) is an enzyme that helps metabolise proteins. It is found in the liver and muscles. AST levels are normally low, but more is released into the blood stream when cells in the liver or muscles are damaged.
  • ALP (Alkaline Phosphatase) is an enzyme found in high amounts in the liver and bones. Its main function is to break down proteins in the body. The level of ALP is raised in the bloodstream when the liver or bones are damaged.
  • GGT (Gamma-glutamyl transferase) is an enzyme that helps transport molecules around the body in addition to helping the liver metabolise drugs and other toxins. GGT levels can become raised due to liver injury or bile duct obstruction.
  • Bilirubin is a waste product which results from the normal breakdown of red blood cells. Bilirubin is removed from the body by the liver, where it is finally released into the stool in bile.

To understand more about what a liver function test shows, see our basic liver test description here.

What is the normal range of liver function tests?

The normal levels of each of the enzyme / protein varies between laboratories and populations but typical ranges for adults in the UK are as follows:

Enzyme / Protein Units Recommended range (Male) Recommended range (Female)
ALT (Alanine Aminotransaminase) IU/L 0-50 0-35
AST (Aspartate aminotransferase) IU/L 0-37 0-31
ALP (Alkaline Phosphatase) IU/L 35-129 35-104
GGT (Gamma-glutamyl transferase) IU/L 0-71 0-42
Bilirubin umol/L 0-20 0-20

Can a blood test detect liver damage?

Abnormal liver function tests may indicate a diagnosis and what further investigations are needed. However, normal results can also be found in people with serious liver disease. Hence it is extremely important that anyone who has symptoms discusses these with their doctor and not try to diagnose problems themselves. Examples of diseases which may produce abnormal results include:

Damage caused by infections:

  • Hepatitis A is a viral illness caused by eating or drinking something that has been contaminated by faecal matter. The severity of symptoms varies from person to person and some people have no symptoms. Usually, the condition goes away by itself within 6 months without long-term harm.
  • Hepatitis B is a viral illness caught from the blood or other bodily fluids from someone with the disease. For example, this might be through unprotected sex, intravenous drug use involving shared needles, accidental needle stick injury or the infection may be passed from mother to baby at birth. Hepatitis B increases the possibility of getting liver cancer and other diseases.
  • Hepatitis C is another viral illness transmitted in the same way as hepatitis B. It usually causes little or no symptoms initially but is often a chronic illness that causes problems 20-30 years later.

Damage caused by drugs, obesity, and alcohol:

  • Cirrhosis is a serious condition caused by a build-up of scars on the liver. Most of the time the condition is irreversible, but if caught early then action can be taken to prevent further damage and increase life expectancy.
  • Fatty Liver Disease (NAFLD) occurs when fat has built up inside the liver. It is usually caused by being overweight or obese. In its early stages it usually causes no problems but it can lead to serious liver problems including cirrhosis. NAFLD increases the risk of diabetes, high blood pressure and kidney disease. According to the NHS up to one in three people in the UK may have early stages of NAFLD.   If NAFLD is detected and managed early it is possible to stop it getting worse and decrease the amount of fat in the liver

What does it mean if your liver function test is high?

Results are considered abnormal when levels fall above or below the normal range. Whilst this may be no cause for concern you must consult your GP to discuss any abnormal result.

What can cause abnormal liver blood test?

Liver function test results that are higher than normal may not always indicate disease, and may in fact be caused by certain lifestyle factors.

Excessive alcohol consumption is a common culprit for abnormal results, as it can raise levels of ALT, AST and GGT in the bloodstream. It is recommended to limit your alcohol consumption to less than 14 units per week in order to maintain good general liver health.

Raised ALP levels can be caused by liver and bone diseases as well as things such as vitamin D deficiencies. A raised GGT levels indicates there is something wrong with the liver for example damage caused by alcohol or certain drugs.

How can I get a liver function test?

At Bluecrest, we offer a range of packages that include liver function tests.

At a clinic

You can book a health check with one of our Certified Healthcare professionals at one of over 2,000 mobile clinics nationwide. All of our Health MOT Packages include a liver function test, in addition to a wide array of health markers for a detailed view of your health. You can choose between 3 levels of testing to suit your own personal needs.

At Home

Alternatively, you can get a liver function test from the comfort of your own home with one of our Home Test Kits, which all include a liver function test and also assess a variety of other key readings pertaining to your general health. All you need to do is order your kit, take your own sample, send it back in our pre-addressed return envelope, and wait to receive your results online within 8 days.