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Summary
What is ALT?
ALT is an enzyme found mostly in the liver although smaller amounts are also found in the kidneys, heart and muscles.
Normally, ALT levels in the blood are low but raised levels often indicate liver injury or inflammation. This usually occurs before more obvious symptoms of liver damage can be seen.
ALT is typically measured as part of Liver Function Tests (LFTs). This is a standard group of tests that is routinely used to check the health of your liver.
Liver Function Tests (LFTs)
LFTs measure enzymes and proteins that are either produced by the liver cells as part of its normal function or released into the blood when liver cells are damaged. Looked at together, along with your symptoms and medical history, they help build a picture of your liver’s health. Either higher or lower than normal levels of these substances can indicate a problem with your liver.
As well as ALT, they measure the enzymes aspartate aminotransferase (AST), alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT) together with bilirubin (a breakdown product from red blood cells that is removed from the body by the liver) and albumin (the most common protein in your blood which is made by your liver).
Measuring ALT is the best way to test for liver damage. Another liver enzyme called AST is also measured in the LFT panel as it too can leak into your bloodstream. However, AST is found in other parts of the body and because of this, ALT is considered to be a better, more direct assessment of liver damage.
Why get tested?
Some conditions that can cause ALT levels to rise from the liver are hepatitis (liver inflammation), alcoholic liver disease, non-alcoholic fatty liver disease, cirrhosis, drugs that cause liver damage (e.g. paracetamol) and liver cancer. Non-liver causes of a raised ALT include heart failure, muscle injury and obesity.
Acute and Chronic Hepatitis
Hepatitis is an inflammation of the liver. There are two major forms: acute and chronic.
| Acute Hepatitis | This is fast-developing and typically makes you feel very ill. In many cases, acute hepatitis causes jaundice - when skin and eyes become yellow and your urine turns brown. It is usually a short term illness. Hepatitis A virus is the most common cause of acute hepatitis. It can also be caused by drugs, alcohol, immune system conditions, and any condition that stops bile being released from your liver. Liver diseases that occur during pregnancy can cause acute hepatitis. |
| Chronic Hepatitis | This is when liver inflammation lasts longer than six months. It usually causes few or no symptoms - typically a loss of energy and tiredness. Most people don’t know that they have it. Chronic hepatitis gradually damages the liver, and this can slowly progress to fibrosis (scarring) and eventually to cirrhosis or liver failure. Chronic hepatitis is usually caused by hepatitis B or C infection but alcoholic liver disease (ALD) and metabolic-dysfunction fatty liver disease (MAFLD), are also major causes. |
Having the test
Sample
Blood.
Any preparation?
None.
Your results
Reading your test report
Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.
| ALT results | Interpretations |
| High levels | Very high levels of ALT (more than 10 times the highest normal level) are usually due to acute (short-term) hepatitis (inflammation of the liver). It is often due to a virus infection. In acute hepatitis, ALT levels usually stay high for about one to two months, but they can take as long as three to six months to return to normal. |
| Normal to moderately high levels | ALT levels are usually not as high in chronic hepatitis, often less than four times the highest normal level. In this case, ALT levels often vary between normal and slightly increased so doctors will repeat the test to see if there is a pattern. People with blocked bile ducts, cirrhosis and liver cancer may have ALT levels that are only moderately raised or close to normal. If you have mild symptoms such as tiredness or loss of energy ALT may be tested to make sure you do not have chronic liver disease. Certain medications and health products may raise ALT levels by causing liver damage in a very small percentage of people taking them. This is true of both prescription drugs and some ‘natural’ or ‘alternative’ health products. |
Reference Intervals
Your results will be compared to reference intervals (sometimes called a normal range).
If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.
| ALT reference intervals | |
| Adult Male | 5 - 40 U/L |
| Adult Female | 5 - 35 U/L |
| The reference intervals for this test are common reference intervals which means that all laboratories in Australia should be using this same target range. | |
Questions to ask your doctor
The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:
More information
Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.
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