ALT Blood Test
Reviewed
Also called: Alanine aminotransferase, Serum Glutamic-Pyruvic Transaminase (SGPT), GPT, Alanine Transaminase
This test measures the amount of ALT (alanine transaminase) in your blood. ALT is an enzyme found mainly in the liver. When liver cells are damaged, they release ALT into the bloodstream. The test is commonly used to help diagnose liver damage or disease and is often part of a group of liver function tests.
Specimen: blood
Why this test may be ordered
- As part of a routine checkup to screen liver health.
- If you have symptoms of liver damage such as nausea, vomiting, lack of appetite, fatigue, weakness, jaundice, abdominal swelling or pain, ankle/leg swelling, dark urine, light-colored stool, or frequent itching.
- If you have a high risk of liver damage due to family history of liver disease, alcohol use disorder, obesity, diabetes, certain medicines that can cause liver damage, or hepatitis or exposure to hepatitis.
Preparation and collection
You may need to stop taking certain medicines before the test; tell your provider about everything you take but do not stop any medicine unless your provider tells you to. An ALT test is usually ordered with other blood tests, and you may need to fast (not eat or drink) for several hours before those tests. Your provider will give you specific instructions.
A health care professional will take a blood sample from a vein in your arm using a small needle. The procedure usually takes less than five minutes.
There is very little risk to having a blood test. You may have slight pain or bruising at the needle site, but most symptoms go away quickly.
Understanding results
Your provider usually compares your ALT results with the results of other liver tests to evaluate your liver health and decide if you need other tests to make a diagnosis. Many things can affect your results, such as your age, sex, weight, certain medicines, dietary supplements, intense exercise, and your menstrual cycle. To learn what your results mean, talk with your provider.
- Lower-than-usual levels of ALT in your blood: Lower-than-usual levels are not common. Your provider may do more tests since this may be a sign of B6 deficiency or chronic kidney disease. Limitation: This result is not a diagnosis by itself; further evaluation is needed. Next step: Talk with your provider about what your result means and whether additional tests are needed.
- Higher-than-usual levels of ALT in your blood: Higher-than-usual levels may be a sign of liver damage from hepatitis, infection, cirrhosis, liver cancer, other liver diseases, a lack of blood flow to the liver, certain medicines (such as cholesterol or pain medicines), or poisons. However, a high level does not always mean you have a medical condition that needs treatment. Limitation: This result is not a diagnosis by itself; many factors can affect ALT levels, and the amount of ALT in your blood is not related to how much your liver may be damaged. Next step: Talk with your provider about what your result means and whether additional tests are needed.
- An ALT blood test alone is not diagnostic; your provider will compare your ALT results with other liver function tests and may need to perform additional tests to make a diagnosis.
- Many factors can affect your results, including age, sex, weight, certain medicines, dietary supplements, intense exercise, and menstrual cycle.
- The amount of ALT in your blood is not related to how much your liver may be damaged.
What to do next
Talk with your provider to understand what your results mean and whether any follow-up tests or actions are needed.
- What do my ALT results mean in combination with my other liver function tests?
- Do I need any additional tests based on my ALT level?
- Should I make any changes to my medicines or lifestyle based on my results?