AST normal range: aspartate aminotransferase levels explained

Quick answer: a normal AST is roughly 8 to 33 U/L (0.13 to 0.55 µkat/L) according to MedlinePlus. Mayo Clinic Laboratories sets its upper limit at 48 U/L for males and 43 U/L for females aged 14 and older, which shows how much the cutoff depends on the lab. Low AST is usually normal. A high AST needs to be read next to ALT: the pattern between the two tells you more than either number alone.

Check AST and ALT at homeAST, ALT and the AST:ALT ratio are on SiPhox Heart & Metabolic, Thyroid Focus, GLP Optimization and Ultimate 360. $124 a test plus $25 shipping.

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AST normal range

AST is reported in units per liter (U/L or IU/L). The reference range depends on the lab's method and population, and Mayo sets separate limits by age and sex:

The ACG guideline on abnormal liver chemistries grades elevations by how many times they exceed the upper limit of normal (ULN): under 5 times, 5 to 15 times, and over 15 times ULN each trigger a different workup. Over 15 times, or an ALT over 10,000 IU/L, prompts checks for acetaminophen toxicity and a sudden loss of blood flow to the liver (ischemic hepatitis).

What AST is

Aspartate aminotransferase is an enzyme that moves amino groups between molecules. It sits inside liver cells, but the ACG notes it is also found in heart muscle, skeletal muscle, kidney and brain. ALT is found mainly in the liver, which makes ALT the more liver-specific of the pair. When cells are damaged, both leak into the blood.

AST is part of the standard liver function test and the comprehensive metabolic panel, alongside ALT, ALP, bilirubin and albumin.

What high AST means

MedlinePlus lists these causes of a high AST:

• Liver disease: hepatitis, cirrhosis, liver cancer and too much iron (hemochromatosis)
• Drugs toxic to the liver, especially alcohol and acetaminophen
• Heart attack or heart procedures, pancreatitis, deep burns and seizures
• Muscle disease or trauma, and mononucleosis

The ACG adds a useful rule: an AST rise without an ALT rise suggests heart or muscle rather than liver. That matters for anyone who trains hard. MedlinePlus notes exercise, pregnancy, some medicines, age and sex can all move results, so a hard workout shortly before a draw can push AST up with a normal ALT. If your AST is mildly high once, a retest after a few quiet days is a reasonable first step; a persistent or large rise needs a doctor.

The AST:ALT ratio

For most liver conditions, including chronic viral hepatitis and fatty liver disease, ALT runs higher than AST, according to the ACG. Alcohol flips the pattern: about 90% of people with alcoholic liver disease have AST above ALT, and more than 70% have a ratio above 2. A ratio of at least 2:1, with neither enzyme above about 300 IU/L, is the classic alcohol pattern, and above 3:1 makes it more likely still. Cirrhosis of any cause can also push AST above ALT, though usually not past 2:1.

Worked example

A 51-year-old man's Mayo-style report shows AST 96 U/L and ALT 40 U/L. His AST is 2 times the upper limit of 48, well under the 5-times line, and his AST:ALT ratio is 96 / 40 = 2.4, the pattern the ACG links to alcohol. A second man has AST 70 U/L and ALT 110 U/L, a ratio of 0.64, the ALT-led pattern more typical of fatty liver disease or viral hepatitis. Both need a doctor's workup, but they start in different places. A third case, AST 75 with a normal ALT of 25 the morning after a heavy leg day, points to muscle and usually just needs a rested retest.

What to test next

Getting a reliable AST result

• Rest before the draw. AST is also found in skeletal muscle (ACG), and MedlinePlus lists exercise among the things that move results. Skip heavy lifting and long endurance sessions for a few days if you want a clean baseline.
• Note alcohol and medicines. Alcohol and acetaminophen are the two liver-toxic drugs MedlinePlus names first. Keep a list of everything you take, including supplements, for whoever reads the result.
• Stay with one lab. The ACG works in multiples of the lab's upper limit, and that limit ranges from 33 to 48 U/L depending on the lab, so a switch can turn a normal result into a high one.
• Pregnancy, age and sex also shift AST (MedlinePlus), so compare yourself with the right range.

At-home tests that include AST

AST is on four SiPhox panels: Heart & Metabolic, Thyroid Focus, Ultimate 360 and GLP Optimization. Each also reports ALT and the AST:ALT ratio. It is not on Longevity Essentials or Hormone Focus.

Heart & Metabolic is the lowest-cost route at $149 per test with shipping, and adds ALP, bilirubin and kidney markers. GLP Optimization ($224) and Ultimate 360 ($274) add GGT, which helps separate liver from bone causes of a high ALP. SiPhox is a wellness service without doctor review, so a high AST goes to your own doctor. More in our SiPhox review.

A note on home samples: SiPhox's partner lab tests capillary blood collected from the upper arm. SiPhox says its results show a 95% to 99% correlation with venous draws in its own quarterly comparisons against Labcorp and Quest, but it has not published a study of the EasyDraw device. If a result would change a treatment decision, confirm it with a venous test through your doctor.

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Everything on the four core panels plus iron studies, B12 and folate, GGT and PSA.

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Track your liver enzymes every quarterAST, ALT, ALP and bilirubin in one upper-arm draw at home. Choose monthly, quarterly or twice-yearly testing.

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