AST Blood Test: Normal Range and What High AST Means

TL;DR

• AST (aspartate aminotransferase, also called SGOT) is an enzyme found mainly in the liver, heart and muscles. When those cells are damaged, AST leaks into the blood.
• A common lab range is about 8–33 U/L, but every lab sets its own. Slightly high results, under twice the upper limit, are common and often come from fatty liver, alcohol, medicines or a hard workout.
• AST isn’t specific to the liver, so it’s always read alongside ALT. A high AST with a normal ALT points away from the liver and toward muscle or the heart.

An AST blood test measures aspartate aminotransferase, an enzyme that leaks into your blood when liver, heart or muscle cells are damaged. A typical normal range is about 8 to 33 U/L, and a slightly high result, like 35, 40 or 42, is common and rarely a sign of serious disease on its own.

That last point is worth holding onto. About 10% of people in the US have raised liver enzymes, and fewer than 5% of them turn out to have serious liver disease, according to a review in American Family Physician. What matters is how high your AST is, whether it stays high and what your ALT is doing. You can type your numbers into the checker above to see where they sit against typical limits.

What Does My AST Number Mean?

The most useful way to read any liver enzyme is as a multiple of the upper limit of normal printed on your report. The American College of Gastroenterology (ACG) grades rises like this:

Your AST vs. your lab’s upper limit	Example if the limit is 33 U/L	What it usually means
At or below the limit	33 or less	Normal range. On its own, it doesn’t rule out liver disease
Up to 2× the limit (borderline)	34–65	Very common. Often fatty liver, alcohol, a medicine or recent hard exercise. Usually rechecked
2–5× the limit (mild)	66–165	Worth a proper look with your doctor to find the cause
5–15× the limit (moderate)	166–495	The ACG says this needs immediate evaluation
More than 15× the limit (severe)	Above 495	Seen with acute hepatitis, drug or toxin injury (such as acetaminophen), poor blood flow to the liver or major muscle breakdown. Needs urgent medical care

Reference ranges differ from lab to lab, so the range printed on your own report always wins over any example here. And no single number is a diagnosis: your doctor will look at the trend and your other results, especially ALT.

What Is AST?

AST is an enzyme that helps cells process amino acids. You’ll find it on a comprehensive metabolic panel or a liver panel, sometimes under its older name, SGOT (serum glutamic-oxaloacetic transaminase).

The key thing to know is where AST lives. According to the ACG guideline, AST is present in the liver and in other organs, including heart muscle, skeletal muscle, kidney and brain. Red blood cells contain it too. ALT, by contrast, is found mainly in the liver. That’s why ALT is the more specific liver marker, and why doctors rarely read AST without it. If you want the other half of the picture, see our guide to the ALT blood test.

What Is a Normal AST Level?

There’s no universal normal. MedlinePlus, from the US National Library of Medicine, gives 8 to 33 U/L as an example range and notes that ranges vary slightly among labs. Some labs set a slightly higher limit for men than for women. U/L (units per liter) and IU/L mean the same thing on a lab report.

Liver specialists also use a lower line than many labs. The American Association for the Study of Liver Diseases (AASLD) notes that an AST or ALT above 30 U/L that persists for 6–12 months may point to chronic liver injury. So a result your lab calls normal can still be worth tracking if it sits in the low 30s year after year.

Reading common results: AST 35, 40, 42 and 45

Here’s how some frequently searched numbers compare with an upper limit of 33 U/L:

Your AST	Multiple of a 33 U/L limit	Plain-English reading
35	About 1.1×	Just above; within range at labs that use a higher limit
40	About 1.2×	Borderline rise
42	About 1.3×	Borderline rise; above the AASLD’s 30 U/L line
45	About 1.4×	Still borderline, under twice the limit

All four are borderline. One result in this zone usually leads to a look at your ALT and a repeat test, not alarm. It becomes more meaningful if it stays raised over months or comes with other abnormal results.

What Causes High AST?

Liver causes

• Fatty liver. MASLD (metabolic dysfunction-associated steatotic liver disease, formerly NAFLD) is the most common cause of mildly raised liver enzymes without symptoms, according to American Family Physician. In fatty liver, ALT is usually higher than AST. Our pillar guide to ALT and AST levels in fatty liver covers this pattern in depth.
• Alcohol. Alcohol-related liver disease classically pushes AST above ALT.
• Medicines and supplements, especially acetaminophen, plus herbal products.
• Viral hepatitis, hemochromatosis (iron overload) and other less common liver conditions.
• Cirrhosis (advanced scarring) from any cause.

Non-liver causes

Because AST lives outside the liver too, plenty of things that have nothing to do with your liver can raise it:

• Hard exercise or muscle injury. The ACG notes that muscle trauma or strenuous sport can raise AST and ALT, mostly AST.
• Heart problems, including a heart attack.
• Breakdown of red blood cells (hemolysis). This can happen in the body, or in the tube if a sample is handled roughly, which can falsely raise AST.
• Thyroid disease, both underactive and overactive.
• Pancreatitis, mononucleosis, burns, seizures, surgery and pregnancy, all listed by MedlinePlus.
• Macro-AST, an uncommon and usually harmless quirk in which AST forms larger complexes in the blood that are cleared more slowly, so the reading stays high.

What If AST Is High but ALT Is Normal?

This pattern points away from the liver. In the ACG guideline’s words, an AST increase without elevation in ALT “is suggestive of cardiac or muscle disease.” Your doctor may order a creatine kinase (CK) test, which rises with muscle damage, and ask about recent workouts, falls or muscle aches.

If both are raised but AST is higher, that’s a different question. Read our guide to the AST/ALT ratio to see what AST running ahead of ALT can mean.

How Hard Exercise Can Skew Your AST

This catches people out. In a small study published in the British Journal of Clinical Pharmacology, healthy men who weren’t used to weightlifting did one hour of it. Their AST and ALT stayed significantly raised for at least 7 days afterward, even though their livers were fine.

So if you had a heavy gym session, a long run or a physically demanding job shift in the week before your test, mention it. A repeat test after a lighter week can tell a workout spike apart from a real liver signal.

What Does a Low AST Mean?

A low AST rarely matters, and many labs don’t flag it at all. Lower readings of both AST and ALT are linked to low vitamin B6, and people with kidney failure on dialysis tend to run lower than others. If yours is below range, it’s worth a quick question to your doctor, but it isn’t a liver warning sign the way a high AST can be.

Should I Retest a High AST?

Usually, yes. The ACG recommends repeating the test or doing a clarifying test to confirm that a result is truly abnormal before starting a full workup.

Don’t expect a retest to make the issue disappear, though. In a UK study of nearly 1,300 primary care patients with abnormal liver enzymes, 84% of results were still abnormal after one month and 75% after two years. A result that stays high deserves a proper look for the cause.

If you have fatty liver or metabolic risk factors, your AST is also one of the four inputs to the FIB-4 score, which estimates liver scarring risk. Our FIB-4 calculator explains how it works.

Before Your Next AST Test

A few simple steps make the result easier to read:

1. Skip unusually hard workouts for about a week before, or tell your doctor if you didn’t.
2. Go easy on alcohol in the days before, and be honest about your usual intake. Our guide on whether alcohol is safe with fatty liver explains why it matters.
3. Bring a list of everything you take, including supplements, herbal products and over-the-counter pain relievers. Don’t stop a prescribed medicine unless your doctor tells you to.
4. Ask for a copy of your results with the lab’s reference ranges, so you can follow your own trend.

Then take these questions to your appointment:

• What was my ALT, and which is higher, AST or ALT?
• Is my AST borderline, mild or higher, as a multiple of the upper limit?
• Could exercise, a medicine or a supplement explain it? Do I need a CK test?
• When should we recheck, and do I need a FIB-4 score or other tests?

The Bottom Line

AST is a useful but non-specific enzyme: it comes from the liver, heart, muscles and red blood cells, so a high result needs context. Borderline rises, under twice the upper limit, are common, and many come from fatty liver, alcohol, medicines or a hard workout. Read your number against your own lab’s range, compare it with your ALT, and treat a persistent rise as a reason for follow-up rather than panic. Very high results, more than 5 times the limit, need prompt medical attention.

Sources

• MedlinePlus: Aspartate aminotransferase (AST) blood test
• Kwo et al. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries (American Journal of Gastroenterology 2017)
• Oh et al. Mildly Elevated Liver Transaminase Levels: Causes and Evaluation (American Family Physician 2017)
• AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease (Rinella et al., Hepatology 2023)
• Pettersson et al. Muscular exercise can cause highly pathological liver function tests in healthy men (British Journal of Clinical Pharmacology 2008)

This article is for informational purposes only and is not medical advice. Talk to your doctor or hepatologist about your specific situation.