Alanine Aminotransferase (ALT)

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).

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.

Can I take the test at home?

There are options for at-home tests of ALT, but it is much more common to have this test done in a medical setting.

Certain at-home test kits include several measurements related to liver health, including ALT. With these tests, you can collect a blood sample at home, but you must mail it to a laboratory where it can be analyzed. At-home tests do not usually require a prescription.

How much does the test cost?

How much an ALT test costs varies. Factors that can influence the cost include whether other measurements are tested along with ALT, where the test is conducted, and whether you have health insurance.

In addition, it is important to know that the total cost associated with the test may be the sum of several different components, including:

• Charges for the technician who draws your blood
• Charges for the laboratory that measures ALT and any other compounds in your blood
• Charges for the office visit when the test is prescribed
• Charges for an office visit to review your test results

These different charges are often paid for by your health insurance company if the test is prescribed by your doctor. However, you may still have out-of-pocket costs like a deductible or copay. Contact the customer care department of your health insurance provider for details about specific expected costs for an ALT test.

An ALT test is conducted with a blood sample, which is obtained using a needle that is inserted into a vein in your arm. This type of blood draw is a routine procedure that is normally done at a doctor’s office or similar medical setting.

In an at-home version of the test, you collect a small blood sample using the provided test materials and then package your sample to be mailed to a laboratory.

Before the test

Because ALT is most commonly tested along with other measurements in a panel, you usually will be told to fast for up to 12 hours before your blood test. During this time, you cannot eat any food and cannot drink anything besides water.

When ALT is tested alone, fasting is not necessary. For this reason, you should check with your doctor about the details of your scheduled test. Follow any instructions from your doctor about fasting beforehand.

Many different types of medications and supplements have the potential to affect your ALT levels. Before the test, you should tell your doctor about any drugs or dietary supplements that you are taking. In some cases, you may be told to stop taking a medication before the test.

Intense exercise also can influence your ALT levels, so tell your doctor ahead of time if you frequently engage in demanding physical workouts.

If you are taking an at-home test, make sure to read the included instructions completely so that you know how to properly carry out each step of the test process.

During the test

A technician or nurse will take a blood sample for your ALT test. They will tie an elastic band around the top part of your arm, which increases blood flow in your veins. They will apply an antiseptic to a small section of your arm and then insert a needle into a vein to withdraw a vial of blood.

The entire process takes only a few minutes. It is normal to feel a brief sting or some throbbing pain when the needle is inserted or removed from your arm.

For at-home tests, blood is taken from your fingertip. The test kit usually includes an antiseptic, a small needle, and special test paper. After cleaning and pricking your fingertip, you can place a drop of blood on the test paper that is then mailed to a lab.

After the test

A blood draw is a common and routine procedure that usually has few side effects. A bandage is normally applied to the puncture site to stop it from bleeding. Some people have bruises or pain in their arm after the test, but these effects are rarely long-lasting.

If you are told to fast before the blood draw, it’s often helpful to bring a snack with you so that you can eat something soon after the test is done. You can usually drive and resume most normal activities once your blood has been drawn.

After an at-home ALT test, you may need to put a bandage on your finger if it doesn’t stop bleeding on its own. Other side effects are rare. After obtaining your blood sample, you will need to properly package it and place it in the mail.

Receiving test results

Results for your ALT test are usually available within a few business days. You may be told of your test results by your doctor’s office. You can also normally obtain a copy of the test report by mail or electronically.

Results from at-home tests of ALT are typically accessed electronically through a smartphone app or a specific website. Getting the results may take a few extra days because of the time it takes for your sample to arrive by mail to the laboratory.

Interpreting test results

The test report should have a line that shows both your ALT level as well as the reference range that the laboratory uses to categorize ALT levels as normal or abnormal. In most cases, ALT will be measured in units per liter (U/L) or international units per liter (IU/L).

When reviewing your results, keep in mind that there is no universal reference range for ALT. There can be variation in laboratory methods that affect what is considered normal. For this reason, it’s important to look at the range provided by the specific lab that analyzed your blood.

Most often, ALT is tested along with other liver enzymes and proteins in a panel test. Your test report will show your levels and the lab’s reference range for each measurement. This is important because your test results are interpreted by looking at these test components together.

High levels of ALT can be a result of damage or injury to cells. Because ALT is most concentrated in the liver, abnormal ALT test results are generally associated with conditions affecting the liver, such as inflammation (hepatitis) and scarring (cirrhosis).

At the same time, ALT can be elevated without any underlying health problem. Multiple factors can affect ALT, and in most cases, high ALT is not a sign of severe liver disease.

In order to interpret your test result, your doctor takes multiple factors into account. These include your current health and health history as well as the levels of other measurements on your test. In addition, your doctor may consider individual factors that can influence your normal level of ALT, including:

• Exercise: Intense or extreme exercise can cause a temporary boost in ALT levels.
• Medications: A number of medications and supplements can alter ALT measurements.
• Sex: Males typically have higher levels of ALT, which is believed to be related to hormonal differences.
• Menstruation: ALT levels can go up or down during the course of the menstrual cycle.
• Age: There is a tendency for ALT levels to decrease with older age, although the exact reason for this is not known.
• Body mass index: Several research studies have found an association between ALT levels and body mass index, which may change the interpretation of test results in people with obesity.

When ALT levels are very high, it may be a sign of an acute liver problem. Mild or moderate elevation, especially if it persists on several tests over time, can be an indicator of a chronic disease. However, the degree of elevation alone is not a reliable predictor of the extent of injury to the liver.

Because many types of liver problems can cause ALT levels to increase, the test alone cannot identify an underlying cause. Although uncommon, ALT can be elevated as a result of disease outside the liver. Looking at how ALT levels relate to other liver enzymes can provide clues that may help the doctor assess your situation and recommend any appropriate follow-up testing.

Your physician can best help you understand the diverse factors that affect the interpretation of your ALT test and what your results mean for your overall health.

Are test results accurate?

Laboratory methods for measuring ALT have been shown to be reliable and reproducible. However, no test is 100% accurate. When errors occur, they are most often related to problems with improperly taking the blood sample.

Do I need follow-up tests?

Follow-up tests are common if an abnormal level of ALT was found on your liver panel or comprehensive metabolic panel test. Further testing may be immediate if you have significantly elevated ALT and/or symptoms of a problem affecting your liver. This follow-up testing may be more thorough and include blood tests, imaging, and in some cases a biopsy.

After an initial abnormal ALT test, repeat testing may be recommended shortly after your first test or at a later date. A series of tests over time may provide a more robust assessment of your liver health and can sometimes avoid the need for more costly or invasive testing.

The most appropriate follow-up depends on your health situation and the interpretation of your test result, and your physician can review the pros and cons of different options for further testing.

Questions for your doctor about test results

A conversation with your doctor about your ALT test can help ensure that you are informed about your results. Some of the following questions may make it easier to cover key information when you talk with your physician:

• What was my ALT level? Was it in the normal reference range?
• Were any other measurements taken? If so, were they normal or abnormal?
• What do the test results mean for my overall health?
• Do you recommend any follow-up tests? If so, which ones and what are their benefits and risks?

Alanine aminotransferase is one of several enzymes produced in the liver that are commonly tested together. The following sections address some similarities and differences between ALT and other related tests.

How is an alanine aminotransferase test different from a liver panel test?

ALT is one of five measurements in the standard liver panel test. The liver panel also usually includes measurements of aspartate aminotransferase (AST), alkaline phosphatase (ALP), albumin, and bilirubin.

It is more common for ALT to be measured in a liver panel than for ALT to be tested individually.

How is alanine aminotransferase different from aspartate aminotransferase (AST)?

Aspartate aminotransferase, also called AST, is another enzyme that is frequently measured in a panel with ALT.

AST and ALT are both referred to as liver enzymes, but there are greater concentrations of AST in other parts of the body like the bones. As a result, ALT is considered to be more directly tied to liver health, but ALT and AST are still typically tested and interpreted together.

How is alanine aminotransferase different from alkaline phosphatase (ALP)?

Alkaline phosphatase, or ALP, is another liver enzyme that is measured in a standard liver panel or comprehensive metabolic panel. ALP is produced and found in the liver, but it is also present in a number of other tissues in the body, including the bones.

ALP and ALK are used to detect different types of liver problems. ALT is an indicator of possible damage to the cells of the liver, and ALP is more often analyzed for its relation to possible blockage of the bile ducts that are inside and outside of the liver.

Because ALP is present in the bones, ALP testing is a better way of detecting bone disorders.

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