What Is an ALT Blood Test?
The alanine aminotransferase (ALT) test is a blood test that checks for liver damage. ALT used to be called serum glutamic-pyruvic transaminase (SGPT). So, it's sometimes called an SGPT test. Your doctor can use this test to see if a disease, drug, or injury has damaged your liver.
Tracking your liver's health is important because of all the things it does for you. Your liver:
- Makes a fluid called bile that helps your body digest food
- Filters your blood to remove wastes and toxins
- Makes substances that help your blood clot
- Stores vitamins and minerals until you need them
- Removes excess sugar from the blood
Toxins (including alcohol), infections, and various illnesses can cause damage to the liver.
Why Is ALT Important?
This enzyme is found mainly in your liver, but smaller amounts of ALT are also present in your muscles, kidneys, and other organs.
Your body uses ALT to break down food into energy. Normally, ALT levels in the blood are low. If your liver is damaged, it will release more ALT into your blood and levels will rise.
But your ALT level alone doesn't give doctors a full picture of your liver health. That's why you often get it along with other liver tests.
Who Gets an ALT Blood Test?
Your doctor might recommend ALT blood testing if you have symptoms of liver disease or damage, such as:
- Stomach pain or swelling
- Yellow skin or eyes (a condition called jaundice)
- Extreme tiredness
- Dark-colored urine
- Light-colored poop
- Itchy skin
You might also get the test if you are at risk for liver damage for any of these reasons:
- You've been exposed to a hepatitis virus.
- You drink a lot of alcohol.
- You have a family history of liver disease.
- You take medicines known to cause liver damage. These include painkillers such as acetaminophen and ibuprofen.
- You are obese.
- You have diabetes.
The ALT test can be done as part of routine blood work, even if your doctor has no special reason for concern. If you've already been diagnosed with liver disease, your doctor can use the ALT test to see how well your treatment is working.
ALT Blood Test Preparation
Your doctor might ask you to stop eating or drinking a few hours before the test. That's because the ALT blood test is often done with other blood tests that require fasting.
Some medicines can affect the results of this test. So, it's important to tell your doctor about any drugs or supplements you take. You might need to change your medication routine before the test, but check with your doctor first.
Intense exercise also can affect results. So, tell your doctor if you plan a vigorous workout before the test.
How Does an ALT Blood Test Work?
A nurse or lab tech will take a sample of your blood, usually from a vein in your arm. They will first tie a band around the upper part of your arm to make your vein fill with blood and swell up. Then, they will clean the area with an antiseptic and place a needle into your vein. Your blood will collect into a vial or tube.
The blood test should take only a couple of minutes. After your blood is taken, the lab tech will remove the needle and band, then put a piece of gauze and a bandage over the spot where the needle was inserted to stop the bleeding.
ALT Blood Test Risks
The ALT blood test is safe. Risks are usually minor and can include:
- Slight pain when the needle is inserted
- Fainting or feeling dizzy
ALT Blood Test Results
You should get your results within a few hours or a few days, depending on the lab your doctor uses. The lab report will tell you whether your ALT numbers fall within a normal range, typically about 7 to 56 units per liter (U/L) of blood. Some labs may use other ranges. Usually, ALT levels are higher in men than in women and children. Levels also tend to be higher in younger people than in older people. People of Mexican-American heritage are also known to have higher ALT levels.
Not everyone with high ALT levels has a medical condition that needs treatment. Fewer than 5% of people with high levels will turn out to have a severe liver condition. Remember that your results could be temporarily abnormal after you take certain medicines or exercise intensely. Even having a menstrual period might change ALT levels.
While a high level of ALT can mean you have liver damage, it can't tell you how bad the damage is. Other tests will help your doctor get a clearer picture.
Here are some of the conditions that could cause high ALT levels:
- Liver damage from alcohol
- Fatty liver disease (too much fat in your liver)
- Too much iron in your body (hemochromatosis)
- Hepatitis (liver inflammation), caused by a virus or an immune system problem
- Cirrhosis (scarring of the liver from any cause)
- Liver cancer
- Poor blood flow to the liver
- Mononucleosis (mono)
A low ALT level is much less common. It usually isn't worrisome, but in some cases, it can be linked to low levels of vitamin B6 or chronic kidney disease. If your level is low, your doctor might have you retake the test or take some other tests.
What Other Tests Will I Take?
ALT usually is done as part of a group of liver function tests called a liver panel.
This panel also includes an aspartate aminotransferase (AST) test. AST is another liver enzyme. As with ALT, the levels of AST in your blood rise if your liver is damaged.
Comparing ALT with AST levels gives your doctor more information about the health of your liver. The AST-to-ASL ratio can help your doctor figure out how severe the liver damage is and what might have caused it.
To find out what type of liver disease you have, your doctor might also test the levels of other enzymes and proteins found in your liver, including:
- Alkaline phosphatase
- Lactate dehydrogenase (LDH)
- Total protein
Talk to your doctor to make sure you understand all of your liver test results. Also, find out how these results might affect your treatment.
An ALT blood test is one of several tests your doctor might order to check your liver health. You might get it because you have symptoms of a liver problem or because you are at risk for liver damage. The results have to be combined with those from other tests to give your doctor a full picture.
ALT Blood Test FAQs
What is the normal range for ALT?
Different labs use different ranges, but the typical range is about 7 to 56 units per liter (U/L) of blood.
What level of ALT is concerning?
Anything above or below the normal range may lead your doctor to order additional tests. But most people with abnormal levels on a single ALT test won't turn out to have a serious health problem.
When should I worry about ALT and AST?
If levels of both enzymes are high, your doctor might say you have elevated liver enzymes. But there's cause for concern only if the levels remain high. In about a third of cases, they return to normal after 2-4 weeks. If they don't, you might get more tests and might need to see a liver specialist.
How do I get my ALT levels down?
If you have a liver condition, getting treatment may lower your ALT levels. Your doctor may order the test repeatedly to see if you are getting better.