Alanine Transaminase (ALT) Blood Test: What It Is, Procedure & Results (2023)

Overview

What is alanine transaminase (ALT)?

Alanine transaminase (ALT), also known as alanine aminotransferase, is an enzyme that’s mainly found in your liver, though it exists in other parts of your body.

An enzyme is a type of protein in a cell that acts as a catalyst and allows certain bodily processes to happen. There are thousands of enzymes throughout your body that have important functions.

What is an ALT blood test?

An alanine transaminase (ALT) blood test measures the amount of ALT in your blood. ALT levels in your blood can increase when your liver is damaged, so healthcare providers often use an ALT blood test to help assess the health of your liver.

Since many types of liver problems can cause ALT levels to increase, healthcare providers don't use the test alone to diagnose conditions. An ALT blood test is most often included in a blood test panel, such as a liver enzyme panel (HFP or LFT) or a comprehensive metabolic panel (CMP). A blood panel measures several aspects of your blood with one sample and can provide more detailed information about your overall health.

Common names for an ALT blood test include:

  • Alanine transaminase (ALT).
  • Alanine aminotransferase.
  • SGPT.
  • Serum glutamic-pyruvic transaminase.
  • GPT.

How is alanine transferase (ALT) different from aspartate transferase (AST)?

Aspartate transferase (AST) is another enzyme that’s commonly measured along with AST in a liver function panel or comprehensive metabolic panel. Both of these enzymes can leak into your bloodstream when certain cells in your body are damaged.

AST and ALT are both commonly considered liver enzymes, but there are greater amounts of AST in other parts of your body, such as your heart, skeletal muscles and pancreas. Because of this, ALT is considered to be more directly tied to your liver health, but healthcare providers use both measurements to assess the health of your liver.

Why do I need an ALT blood test?

The purpose of an ALT blood test is to help evaluate the health of your liver. If cells in your liver are damaged, it can cause ALT to leak into your blood, so an ALT blood test can help find liver issues.

Your healthcare provider may order a blood panel test that includes an ALT test for you to help screen for, monitor or help diagnose liver conditions.

Screening

Screening means checking for potential health issues before you experience symptoms. Your healthcare provider will likely recommend screening with a liver panel blood test that includes an ALT test if you have risk factors for liver disease, which include:

  • Heavy alcohol use.
  • Family history of liver disease.
  • Diabetes.
  • Obesity.
  • Injecting drugs using shared needles.

Since ALT tests are often included in routine blood panel tests that assess your general overall health, such as a comprehensive metabolic panel (CMP), you may have an ALT test even if you don’t have risk factors for liver disease.

Monitoring

If you have a liver condition, your provider may order an ALT test, often as part of a panel, to monitor your condition to see if it’s improving, worsening or staying the same with or without treatment. Your provider may also have you undergo an ALT test and liver enzyme panel test if you’re taking a medication that can affect your liver health.

Diagnosing

Your provider may use an ALT test for diagnostic purposes when you’re experiencing signs and symptoms of possible liver problems. While providers can’t diagnose a condition based solely on ALT levels, it can be an important part of the diagnostic process.

Signs and symptoms of liver conditions include:

  • Nausea and/or vomiting.
  • Belly (abdominal) pain.
  • Itchy skin.
  • Jaundice (a yellowing of your skin and the whites of your eyes).
  • Tiredness (fatigue).
  • Appetite loss.

Test Details

Who performs an ALT blood test?

A healthcare provider called a phlebotomist usually performs blood draws, including those for an ALT blood test, but any healthcare provider trained in drawing blood can perform this task. The samples are sent to a lab where a medical laboratory scientist prepares the samples and performs the test on machines known as analyzers.

Do I need to fast for an ALT blood test?

If your ALT test is part of a comprehensive metabolic panel (CMP), you’ll likely need to fast for 10 to 12 hours before your CMP blood test. Fasting means not eating or drinking anything other than water.

It’s not as common, but if you’re only getting an ALT blood test, you don’t need to fast.

In any case, your healthcare provider will give you instructions when they order the bloodwork. Be sure to follow their directions.

Do I need to do anything to prepare for an ALT blood test?

Many different types of medications and supplements can affect your ALT levels, so it’s important to tell your healthcare provider about any drugs or dietary supplements you’re taking before you get the test. In some cases, your provider may have you stop taking a medication before the test. Only stop taking medication if your provider tells you to do so.

Intense exercise can also affect your ALT levels, so tell your provider if you frequently do demanding physical workouts before you get the ALT test.

What should I expect during my ALT blood test?

You can expect to experience the following during a blood test, or blood draw:

  • You’ll sit in a chair, and a healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
  • Once they’ve located a vein, they’ll clean and disinfect the area.
  • They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
  • After they insert the needle, a small amount of blood will collect in a test tube.
  • Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop any bleeding.
  • They’ll place a bandage over the site, and you’ll be finished.

The entire procedure usually takes less than five minutes.

What should I expect after my ALT blood test?

After a healthcare provider has collected your blood sample, they’ll send it to a laboratory for testing. Once the test results are back, your healthcare provider will share the results with you.

What are the risks of an ALT blood test?

Blood tests are a very common and essential part of medical testing and screening. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.

When can I expect the results of my ALT blood test?

In most cases, you should have your test results within one to two business days, though it could take longer.

Results and Follow-Up

What do the results of an ALT blood test mean?

Blood test reports, including alanine transaminase (ALT) test reports, usually provide the following information:

  • The name of the blood test or what was measured in your blood.
  • The number or measurement of your blood test result.
  • The normal measurement range for that test.
  • Information that indicates if your result is normal or abnormal or high or low.

What is the normal range for an ALT blood test?

The normal range for alanine transaminase (ALT) varies from laboratory to laboratory. One common reference range for an ALT blood test is 7 to 56 U/L (units per liter). ALT levels are typically higher in people assigned male at birth than in people assigned female at birth.

Since ranges can vary depending on the laboratory, it’s important to check your test result report to see what your specific lab’s reference range is.

What does it mean if my alanine transaminase (ALT) is high?

High levels of ALT in your blood can be due to damage or injury to the cells in your liver. An increased ALT level may indicate the following conditions:

  • Alcohol-induced liver injury.
  • Fatty liver disease (too much fat in your liver).
  • Hepatitis (liver inflammation).
  • Cirrhosis (scarring of the liver).
  • Taking medications that are toxic to your liver.
  • Liver tumor or liver cancer.
  • Liver ischemia (not enough blood flow to your liver, which leads to death of liver tissue).
  • Hemochromatosis (having too much iron in your body).
  • Mononucleosis ("mono").
  • Certain genetic conditions can affect your liver.

Although it’s less common, elevated ALT levels can also indicate injury to cells in other parts of your body, since ALT isn’t solely found in your liver.

It’s important to know that having a high ALT test result doesn't necessarily mean you have a medical condition. Less than 5% of people with elevated ALT levels have severe liver conditions. Other factors can affect your ALT levels. Your provider will take into consideration several factors, including other blood test results and your medical history, when analyzing your results.

What does it mean if my alanine transaminase (ALT) is low?

Having a lower than normal ALT result is uncommon and usually isn’t a cause for concern. However, a lower than normal ALT level could indicate a vitamin B6 deficiency or chronic kidney disease.

If your ALT result is lower than what's considered normal, your healthcare provider will likely have you retake the test or undergo further testing to make sure nothing is causing your low level.

Should I be worried if I have high or low alanine transaminase (ALT) test results?

If your ALT test result is high or low, it doesn't necessarily mean that you have a medical condition that needs treatment. Other factors can affect your levels, including:

  • Exercise: Intense or extreme exercise can cause a temporary increase in ALT levels.
  • Medications: Several medications and supplements can affect ALT levels, including over-the-counter pain medications such as acetaminophen.
  • Sex: Scientists believe hormonal differences contribute to sex differences in ALT levels.
  • Menstruation: ALT levels can increase or decrease during your menstrual cycle.
  • Age: ALT levels tend to decrease with older age.
  • Heritage: Research shows that people who have Mexican-American heritage are more likely to have elevated levels of ALT.
  • Body mass index: Several studies have revealed an association between ALT levels and body mass index (BMI), which may change the interpretation of test results in people who have obesity.

In addition to the above factors, when analyzing your ALT results, your healthcare provider will take into consideration many aspects of your health and situation, including:

  • Your medical history.
  • How high or low your ALT results are.
  • Previous ALT results.
  • The results of other tests usually taken alongside ALT.
  • If you’re experiencing symptoms.

Do I need follow-up tests if my ALT results are abnormal?

It’s common for healthcare providers to recommend follow-up tests if you have an abnormal ALT level.

Follow-up testing may include:

  • Repeat ALT blood tests.
  • Other blood tests.
  • Imaging tests.
  • A biopsy.

Additional testing may be immediate if you have significantly elevated ALT levels and/or are experiencing symptoms of a liver condition.

Every person and situation is unique, so there’s no single follow-up testing plan that works for everyone. Together, you and your provider will determine the best plan.

When should I call my doctor?

If you’re experiencing symptoms of liver damage, such as jaundice or belly pain, call your healthcare provider.

If you’ve been diagnosed with a liver condition and are experiencing new or concerning symptoms, contact your provider.

If you have any questions about your alanine transaminase (ALT) results, don’t be afraid to ask your provider questions.

A note from Cleveland Clinic

Seeing an abnormal test result can be stressful. Know that having a high level of alanine transaminase (ALT) doesn’t necessarily mean you have a medical condition and need treatment. Many factors can affect your ALT levels, and 1 in 20 healthy people will have results outside of the normal range. Your healthcare provider will let you know if you need to undergo further tests to determine the cause of the abnormal level. Don’t be afraid to ask your provider questions. They’re there to help you.

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