Alanine aminotransferase (ALT) Test
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The alanine aminotransferase (ALT) test is a blood test in which a sample is drawn from a vein to measure levels of the liver enzyme ALT. It is used to detect and monitor liver damage or inflammation, as elevated ALT levels can indicate liver disease.
Why get tested?
To screen for liver disease
When to get tested?
If your doctor thinks that you have symptoms of a liver disorder
Sample required?
A blood sample will be taken from a vein in the arm
Test preparation needed?
No test preparation is needed, although you should inform your doctor about any drugs you are taking
Common questions
The ALT blood test detects liver injury. ALT results are usually assessed alongside the results of other blood tests such as alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT) and aspartate aminotransferase (AST) to help determine which form of liver disease is present.
A doctor usually requests an ALT test with other laboratory investigations to evaluate a patient who has symptoms of a liver disorder. ALT is used to identify liver damage. Some of these symptoms include jaundice, dark urine, nausea, vomiting, abdominal swelling, unusual weight gain and abdominal pain. ALT can also be used, either by itself or with other tests, for patients at risk of developing liver disease such as:
- persons who have a history of known or possible exposure to hepatitis viruses
- those who drink too much alcohol
- those whose family have a history of liver disease
- people who take drugs that might damage the liver
- those who are overweight or who have diabetes
In people with mild symptoms, such as tiredness or loss of energy, ALT may be tested to make sure they do not have chronic (long-term) liver disease. ALT is often used to monitor the treatment of persons who have liver disease to see if the treatment is working and may be requested either by itself or along with other blood tests.
Very high concentrations of ALT (more than 10 times the highest normal level) are usually due to acute (short-term) hepatitis, often due to a viral infection. In acute hepatitis, the concentration of ALT usually stays high for about 1–2 months but can take as long as 3–6 months to return to normal.
ALT concentrations are usually not as high in chronic hepatitis, often less than 4 times the highest normal level. In this case, ALT concentrations often vary between normal and slightly increased, so doctors may request the test frequently to see if there is a pattern. A moderately high ALT can also occur when there is a high alcohol intake, diabetes or raised serum triglycerides, all of which can cause fatty liver.
In some liver diseases, especially when the bile ducts are blocked (cholestasis), when a person has cirrhosis or when liver cancer is present, the concentration of ALT may be close to normal.
An injection of medicine into the muscle tissue or strenuous exercise may increase ALT concentration as it is released into the bloodstream from muscle.
Certain drugs may cause liver damage, resulting in high ALT concentrations. This occurs in a very small percentage of patients and is true of both prescription drugs and some ‘natural’ health products. If your doctor finds that you have a high ALT, tell them about all the drugs and health products you are taking.
Hepatitis is an inflammation of the liver. There are two major forms: acute and chronic. Acute hepatitis is a fast-developing disease and typically makes affected persons feel sick, as if they have the flu, often with loss of appetite and sometimes diarrhoea and vomiting. In many cases, acute hepatitis causes dark urine, pale stools and yellowing of the skin and eyes (jaundice). Most affected individuals eventually recover completely. Chronic (long-term) hepatitis usually causes no symptoms or causes only loss of energy and tiredness; most people don’t know that they have it. In some people, chronic hepatitis can gradually damage the liver and, after many years, cause it to fail.
Other commonly used liver tests include other enzymes found in liver cells, such as aspartate aminotransferase (AST) and alkaline phosphatase as well as bilirubin, which is a breakdown product from red blood cells removed from the body by the liver and spleen. The doctor will often order these tests together as a group and refer to them as ‘liver function tests’. Albumin is also frequently included in the liver function test profile because, as albumin is produced by the liver, it can be used as a measure of liver protein synthesis. However, other factors can affect the concentration of albumin in the blood such as poor nutrition or excessive loss from the gut or kidney.