Liver Function Tests (LFTs) may be used to screen a person for liver damage, especially someone who has a condition, or is taking a drug, that may affect the liver.

LFTs or one or more component tests may be used to help detect liver disease if a person has symptoms that indicate possible liver dysfunction or if a person is being monitored or treated for a known condition or liver disease. A bilirubin test, for instance, may be ordered to evaluate and monitor a jaundiced newborn.

Abnormal tests on a liver function tests panel may prompt a repeat analysis to see if the elevation or decrease persists and/or may indicate the need for additional testing to determine the cause of the liver dysfunction.

The group of tests may also be ordered to monitor liver function and the effectiveness of treatment in someone who has a liver disease.

LFTs, or one or more components, may be ordered when someone is at risk for liver dysfunction. Some examples include:

• people who have a history of known or possible exposure to hepatitis viruses
• those who are heavy alcohol drinkers
• individuals whose families have a history of liver disease
• people who take drugs that might occasionally damage the liver

LFTs may be ordered when a person has signs and symptoms of liver disease. Some of these include:

• Weakness, fatigue
• Loss of appetite
• Nausea, vomiting
• Abdominal swelling and/or pain
• Jaundice
• Dark urine, light coloured stool
• Itching (pruritus)

Usually no one single set of liver tests are used to make a diagnosis. Often, several LFTs will be ordered over a few days or weeks to determine if a pattern is present and to help determine the cause of the liver disorder.

When liver disease is detected, it may be monitored on a regular basis over time with the LFTs or with one or more of its components. LFTs may also be ordered regularly to monitor the effectiveness of treatment for the liver disorder.

LFT results are not diagnostic of a specific condition; they indicate that there may be a problem with the liver. In a person who does not have symptoms or identifiable risk factors, abnormal liver test results may indicate a temporary liver injury or reflect something that is happening elsewhere in the body – such as in the skeletal muscles, pancreas, or heart. It may also indicate early liver disease and the need for further testing and/or periodic monitoring.

Results of LFTs are usually evaluated together. Several sets of results from tests performed over a few days or weeks are often assessed together to determine if a pattern is present. Each person will have a unique set of test results that will typically change over time. A doctor evaluates the combination of liver test results to gain clues about the underlying condition. Often, further testing is necessary to determine what is causing the liver damage and/or disease.

The table below shows examples of some combinations of results that may be seen in certain types of liver conditions or diseases.

If a person is taking drugs that may affect their liver, then abnormal test results may indicate a need to re-evaluate the dosage or choice of medication. When a person with liver disease is being monitored, then the doctor will evaluate the results of the liver panel together to determine if liver function in worsening or improving. For example, increasingly abnormal bilirubin, albumin, and/or PT may indicate a deterioration in liver function, while stable or improving results of these tests may indicate liver function preservation or improvement.

For individual tests:

Alanine aminotransferase (ALT)
A very high level of ALT is frequently seen with acute hepatitis. Moderate increases may be seen with chronic hepatitis. People with blocked bile ducts, cirrhosis, and liver cancer may have ALT concentrations that are only moderately elevated or close to normal.

Alkaline phosphatase (ALP)
ALP may be significantly increased with obstructed bile ducts, liver cancer, and also with bone disease.

Aspartate aminotransferase (AST)
A very high level of AST is frequently seen with acute hepatitis. AST may be normal to moderately increased with chronic hepatitis. In people with blocked bile ducts, cirrhosis, and liver cancer, AST concentrations may be moderately increased or close to normal. When liver damage is due to alcohol, AST often increases much more than ALT (this is a pattern seen with few other liver diseases). AST is also increased after heart attacks and with muscle injury.

Bilirubin
Bilirubin is increased in the blood when too much is being produced, less is being removed, due to bile duct obstructions, or to problems with bilirubin processing. It is not uncommon to see high bilirubin levels in newborns, typically 1 to 3 days old.

Albumin
Albumin is often normal in liver disease but may sometimes be low due to decreased production.

Total Protein
Total protein is typically normal with liver disease.

Gamma-glutamyl transferase (GGT)
A GGT test may be used to help determine the cause of an elevated ALP. Both ALP and GGT are elevated in bile duct and liver disease, but only ALP will be elevated in bone disease. Increased GGT levels are also seen with alcohol consumption and often in patients taking some drugs that are metabolized in the liver such as carbamazepine and phenobarbitone.

Prothrombin Time (PT)
A prolonged or increased PT can be seen with liver disease, vitamin K deficiency, and with coagulation factor deficiencies.

In order to diagnose a liver disease, a doctor will evaluate the liver panel test results, order follow-up tests such as hepatitis testing, and may order a liver biopsy and/or imaging scans to help confirm a diagnosis and determine the extent of liver damage.

Many over-the-counter drugs and herbal or dietary supplements have the potential to affect the liver. Excessive paracetamol use and the combination of paracetamol and alcohol for instance can cause severe liver damage, as can exposure to toxins such as poisonous mushrooms.

Yes, early liver disease often causes no symptoms or mild nonspecific symptoms, such as fatigue and nausea.

Yes, many temporary conditions, such as shock, burns, severe infections, muscle trauma, dehydration, pancreatitis, haemolysis, and pregnancy can cause one or more of the liver function tests to be abnormal.

Some liver conditions, such as haemochromatosis and Wilson's disease, may be inherited. Early detection of these conditions allows them to be treated and managed appropriately.

Depending on the results of the liver panel and other factors such as signs, symptoms and clinical and family history, a doctor may suspect a particular cause of liver disorder and order follow-up tests. Some examples include: