Alanine aminotransferase, usually referred to as ALT, is an enzyme that is concentrated primarily in the liver. Enzymes are proteins that facilitate important functions in the body.
An ALT test measures the amount of this enzyme in the blood. ALT levels can increase when liver cells are damaged, so the test can be used to evaluate the condition of the liver.
In general, ALT is not tested alone. Instead, it is usually measured along with other liver enzymes as part of a panel test like the liver panel or comprehensive metabolic panel (CMP).

Purpose of the test

The purpose of an ALT test is to help assess the health of the liver. Damage to cells in the liver can cause ALT to leak into the blood, so an ALT test can help detect liver problems.
ALT is commonly tested with other liver enzymes and compounds in the blood. Together, these measurements can be used for diagnosis, screening, and monitoring.

Diagnosis is testing that happens after symptoms have started. Its goal is to find the problem or cause for symptoms. ALT testing may be useful in the diagnosis of symptoms that can be tied to liver problems like nausea and vomiting, abdominal pain, itching, jaundice, fatigue, and appetite loss.

Screening is testing to try to find health problems before any symptoms have occurred. With some liver conditions, ALT levels may rise in the blood before symptoms begin, so testing for ALT and other liver enzymes may be prescribed for early detection. Screening is more likely to be recommended if you have risk factors for liver disease such as heavy alcohol use, diabetes, obesity, or a family history of liver problems. Even if you don’t have risk factors, your doctor may prescribe tests that measure ALT during routine health check-ups.

Monitoring includes all the methods that are used to keep track of how your condition progresses. If you have had liver disease or an abnormal ALT test before, ongoing testing may be used to see how your levels change over time. ALT and liver enzyme tests can also monitor for side effects of medications that can affect liver health and function.

What does the test measure?

An ALT test measures the level of this enzyme, alanine aminotransferase, in your blood.
ALT is one of several enzymes that help the liver function properly. Although small amounts of ALT can be found in other parts of the body, it is predominantly found in the liver.
In most cases, ALT is not measured by itself. Instead, ALT is normally one of several measurements in a liver panel or comprehensive metabolic panel. Taking multiple measurements along with ALT provides more context for evaluating liver health.

When should I get an alanine aminotransferase test?

ALT testing is appropriate in a range of different medical circumstances. It is often prescribed as an initial diagnostic test if you have symptoms that could be explained by an underlying problem affecting your liver.

Even if you have general symptoms, a panel test that includes ALT may be used in the diagnostic process. The liver panel or comprehensive metabolic panel, which both include ALT, may be part of a basic evaluation in urgent care or the emergency room.

As a tool for early detection of liver disease, ALT can be periodically measured with other liver enzymes even if you don’t have any symptoms. Your doctor may recommend screening involving ALT if you are at higher risk of liver disease.

ALT testing may also be included in your typical medical check-ups, although data is limited to show that widespread screening offers more benefits than downsides, which can include added medical costs and unnecessary medical procedures.

Follow-up ALT testing can be used if you’ve had a previous test with an abnormal result. If you’ve been diagnosed with liver disease in the past, repeated ALT testing can help monitor the progression of the disease. When your doctor is prescribing a medication that can affect your liver, ALT testing can be a tool to watch for unwanted side effects.

How to get tested

Testing for alanine aminotransferase is normally done as part of a panel of measurements that is prescribed by a physician. The ALT test is performed on a blood sample that is typically taken from a vein in your arm in a hospital, laboratory, clinic, or doctor’s office.