The ALT test detects liver injury. ALT values are usually assessed alongside other liver function tests, such as total protein, albumin, alkaline phosphatase (ALP) 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 is at risk of or has symptoms of a liver disorder. 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:

• 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.

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 ordered either by itself or along with other tests.

Very high levels of ALT (more than 10 times the highest normal level) are usually due to acute (short-term) hepatitis, often due to a virus infection. In acute hepatitis, ALT levels usually stay high for about 1–2 months, but can take as long as 3–6 months to return to normal.

ALT levels are usually not as high in chronic hepatitis, often less than 4 times the highest normal level: in this case, ALT levels often vary between normal and slightly increased, so doctors will order the test frequently to see if there is a pattern. In some liver diseases, especially when the bile ducts are blocked, or when a person has cirrhosis, ALT may be close to normal levels.

Adult

Male         5 - 40 U/L
Female     5 - 35 U/L

The reference intervals shown above are known as a harmonised reference interval. This means that eventually all laboratories in Australia will eventually use this same interval so wherever your sample is tested, the reference interval should be the one shown above. Laboratories are in the process of adopting these harmonised intervals so it is possible that the intervals shown on the report of your results for this test may be slightly different until this change is fully adopted. More information can be found under Reference Intervals – An Overview.

Certain drugs may raise ALT levels by causing liver damage in a very small percentage of patients taking the drug. This is true of both prescription drugs and some ‘natural’ health products. If your doctor finds that you have a high ALT, tell him or her 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 turns urine brown, and colours the skin and eyes yellow. 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), gamma-glutamyl transferase (GGT) and alkaline phosphatase (ALP), as well as bilirubin (a breakdown product from red blood cells removed from the body by the liver and spleen) and albumin (a protein produced by the liver). The doctor will often order these tests together as a group and refer to them as 'liver function tests'.