ALT Liver Test Results Explained: What High ALT (and AST) Means

Plain-English guide · Last updated October 20, 2026 · Based on NIH and U.S. government sources

The short answer: A high ALT means more of this liver enzyme than usual has leaked into your blood, which can be a sign that liver cells are irritated or damaged. Common reasons include fatty liver, alcohol, hepatitis and some medicines or supplements, but a single high result doesn't always mean you have a condition that needs treatment, so your doctor will look at it with your other tests.

What ALT and AST are

ALT (alanine transaminase, also called SGPT) is an enzyme found mainly in your liver. Normally only small amounts are in your blood. When liver cells are damaged, they release ALT into the bloodstream (MedlinePlus).

AST (aspartate aminotransferase, also called SGOT) is a related enzyme. It is found mainly in the liver but also in the heart, muscles and other tissues (MedlinePlus). Because ALT is found mostly in the liver, it is a more specific check for liver damage. The two are usually measured together as part of liver function tests, often within a comprehensive metabolic panel (CMP) (MedlinePlus).

Normal ALT and AST ranges

Ranges vary slightly from lab to lab, so always compare your result with the range printed on your report. The MedlinePlus Medical Encyclopedia lists these typical ranges (MedlinePlus ALT, MedlinePlus AST):

Source: MedlinePlus Medical Encyclopedia. U/L means units per liter. Your lab's range may differ.
Test	Typical normal range
ALT	4 to 36 U/L
AST	8 to 33 U/L

Many things can affect results, including age, sex, weight, certain medicines and dietary supplements, intense exercise and, for ALT, where you are in your menstrual cycle (MedlinePlus). The amount of ALT in your blood also isn't a direct measure of how much the liver is damaged.

What a high or low ALT may mean

These are possible causes, not a diagnosis. Your provider usually compares ALT with your other liver tests and may order more tests before reaching any conclusion.

Possible reasons for a high ALT

MedlinePlus lists these possible causes (MedlinePlus, MedlinePlus Medical Encyclopedia):

Too much fat in the liver (fatty liver)
Hepatitis (an inflamed liver) or other infections, including mononucleosis
Medicines and substances that can be hard on the liver, such as alcohol or acetaminophen, and certain cholesterol or pain medicines
Too much iron in the body (hemochromatosis). See our ferritin guide.
Cirrhosis (scarring), reduced blood flow to the liver, pancreatitis, or a liver tumor

High AST

AST can rise from liver problems, but also from heart problems, pancreatitis, deep burns, seizures, surgery and other causes, because it is found outside the liver too (MedlinePlus).

Low ALT

A lower-than-usual ALT is not common. MedlinePlus says your provider may check further, since it can be a sign of vitamin B6 deficiency or chronic kidney disease. Low AST is usually considered normal (MedlinePlus, MedlinePlus).

Fatty liver: a common root cause

Nonalcoholic fatty liver disease (NAFLD), now also called metabolic dysfunction-associated steatotic liver disease (MASLD), is a buildup of fat in the liver not caused by heavy drinking. The NIDDK estimates about 24% of U.S. adults have it, and it is one of the most common causes of liver disease in the United States (NIDDK). It is often silent, with few or no symptoms (NIDDK).

You are more likely to develop it if you have overweight or obesity, insulin resistance or type 2 diabetes, high triglycerides or unhealthy cholesterol levels, or metabolic syndrome (NIDDK). See our cholesterol guide and fasting glucose guide.

Plant-based, liver-friendly steps to discuss with your doctor

For fatty liver, the NIDDK says losing at least 3% to 5% of body weight can reduce liver fat, and 7% to 10% may be needed to reduce inflammation and scarring. Physical activity helps even without weight loss. Weight loss should be gradual, because rapid weight loss can make liver disease worse (NIDDK). Diet changes the NIDDK describes fit well with whole plant foods (NIDDK):

Choose low-glycemic whole foods such as most fruits, vegetables and whole grains, over white bread and white rice.
Cut sugary drinks such as soda, sports drinks, sweetened tea and juice, which are major sources of fructose.
Swap saturated and trans fats for unsaturated fats, such as nuts, seeds and plant oils, including plant omega-3 sources like walnuts and ground flaxseed.
Watch portion sizes and keep a healthy weight.
Limit alcohol, which can further damage the liver.

Herbs and supplements: be careful

The NIDDK advises talking with your doctor before using dietary supplements for fatty liver, noting that some herbal remedies can actually damage your liver (NIDDK).

Milk thistle (silymarin): often marketed for the liver, but NCCIH says clinical trial results for liver diseases have been conflicting or too limited, and two NCCIH-funded studies, in hepatitis C and in NASH, did not show benefit. It appears well tolerated but can cause digestive upset and allergic reactions, and product quality varies (NCCIH).
Turmeric and curcumin: NCCIH says there isn't enough evidence to conclude they help, and highly absorbable curcumin products may harm your liver (NCCIH).

If your ALT is high, bring every supplement and herbal product you take to your appointment. NCCIH recommends discussing supplements with your providers, especially if you take medicines (NCCIH).

Medicines and safety notes

Don't stop a medicine on your own because your ALT is high, even if it is a medicine known to affect the liver. MedlinePlus advises not stopping any medicine unless your provider tells you to (MedlinePlus). Your prescriber can decide whether a change is needed.
Acetaminophen: MedlinePlus warns that taking too much acetaminophen can cause liver damage, sometimes serious. Follow the label, don't take more than one product containing acetaminophen at a time, and ask your doctor or pharmacist how much is safe for you, especially if you have liver disease or drink alcohol (MedlinePlus).

When to talk to your doctor

Your ALT or AST is flagged high, especially if it stays high on a repeat test.
You have yellowing skin or eyes (jaundice), dark urine, light-colored stools, belly pain or swelling, nausea, ongoing itching or unusual tiredness (MedlinePlus).
You drink alcohol regularly, have diabetes or obesity, have a family history of liver disease, or may have been exposed to hepatitis.
You feel very unwell, confused, or are vomiting blood. Call 911 or seek emergency care.

Questions to ask at your next appointment

How high is my ALT compared with my AST and other liver tests?
Could fatty liver, alcohol, a medicine or a supplement be causing this?
Do I need hepatitis testing, an ultrasound or other follow-up?
How much weight loss or activity would help my liver?
When should I retest?

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Frequently asked questions

What does high ALT mean?

A high ALT means more of this liver enzyme has leaked into your blood, which can be a sign of liver irritation or damage from causes such as fatty liver, hepatitis, alcohol or certain medicines. MedlinePlus notes a high result doesn't always mean you have a condition that needs treatment, so talk with your doctor.

What is a normal ALT level?

The MedlinePlus Medical Encyclopedia lists a normal ALT range of 4 to 36 U/L, and a normal AST range of 8 to 33 U/L. Ranges vary slightly between labs, so compare your result with the range on your report.

What is the difference between ALT and AST?

Both are enzymes released when cells are damaged. ALT is found mainly in the liver, so it is a more specific liver test. AST is also found in the heart, muscles and other tissues, so it can rise for non-liver reasons too.

Can exercise raise ALT?

Yes. MedlinePlus says intense exercise can affect ALT results, along with age, sex, weight, some medicines and supplements, and the menstrual cycle. Tell your provider if you had a hard workout before your test.

Does milk thistle lower ALT?

NCCIH says studies of milk thistle for liver diseases have been conflicting or too limited to draw conclusions, and two NCCIH-funded trials did not show benefit. The NIDDK warns some herbal remedies can damage the liver, so talk with your doctor before trying any supplement.

Sources

Medical disclaimer: This article is general education, not medical advice. It does not diagnose, treat, cure or prevent any disease. Always talk with your doctor about your lab results, and talk with your prescriber before starting, stopping or changing any medicine or supplement. If you think you have a medical emergency, call 911. Last updated October 20, 2026.