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AST blood test

Aspartate aminotransferase

In short

A typical adult AST result is 8 to 43 U/L for women and 8 to 48 U/L for men. A small rise is common and often passes. When ALT is in range, the extra AST often comes from muscle, especially after hard exercise. Always read your result against the range printed on your own report.

An enzyme found in the liver, muscles and heart.

AST is found in the liver, and also in muscles, the heart and the kidneys. When any of these are strained or injured, AST leaks into the blood. Doctors read it next to ALT, which comes mostly from the liver, to see where a rise comes from.

Is my AST high or low?

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Typical range

ForRangeUnit
Female8–43U/L
Male8–48U/L

Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.

If your AST is high

A small rise is common and often passes. When ALT is in range, the extra AST often comes from muscle, especially after hard exercise.

Common reasons

  • Hard exercise or a muscle strain in the days before the test
  • Extra fat stored in the liver, often with weight gain
  • Regular heavy drinking, which tends to raise AST more than ALT
  • Some medicines and supplements, including some pain relievers
  • A recent viral infection, such as mono (mononucleosis)
  • Less often: a muscle disease or a large muscle injury
  • Less often: liver inflammation (hepatitis), liver scarring (cirrhosis) or a heart problem

If your AST is low

A low AST is usually not a concern, and doctors rarely act on it.

Common reasons

  • Normal variation between people
  • Low vitamin B6, which AST needs to work
  • Long-term kidney disease or dialysis

What can throw it off

Hard exercise, especially weight training, can raise AST for several days afterward.

Questions to take to your appointment

  1. 1Could exercise or a muscle strain explain this?
  2. 2Is my ALT up too, or only my AST?
  3. 3Should my CK, a muscle test, be checked too?

Read together with

Doctors rarely read AST alone. These usually sit next to it.

Quick answers

What is the AST blood test?

AST (Aspartate aminotransferase): An enzyme found in the liver, muscles and heart. AST is found in the liver, and also in muscles, the heart and the kidneys. When any of these are strained or injured, AST leaks into the blood. Doctors read it next to ALT, which comes mostly from the liver, to see where a rise comes from.

What is a normal AST level?

For most adults, AST is typically 8 to 43 U/L for women and 8 to 48 U/L for men. Labs differ a little, so the range printed next to your result is the one to go by.

What does a high AST mean?

A small rise is common and often passes. When ALT is in range, the extra AST often comes from muscle, especially after hard exercise. Common reasons include hard exercise or a muscle strain in the days before the test; extra fat stored in the liver, often with weight gain; regular heavy drinking, which tends to raise AST more than ALT; and some medicines and supplements, including some pain relievers. A doctor reads it together with your other results and how you feel.

What does a low AST mean?

A low AST is usually not a concern, and doctors rarely act on it. Common reasons include normal variation between people; low vitamin B6, which AST needs to work; and long-term kidney disease or dialysis.

What can affect my AST result?

Hard exercise, especially weight training, can raise AST for several days afterward.

What should I ask my doctor about my AST?

Questions worth taking to the appointment: Could exercise or a muscle strain explain this? Is my ALT up too, or only my AST? Should my CK, a muscle test, be checked too?

What this page can’t do

It reads each number on its own.

Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.

It doesn't know you.

Your age, your medicines, how you feel and your last result all change what a number means.

It doesn't remember.

Close this page and your results are gone. That's on purpose: nothing was ever sent to us.

We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.

Vita: Health Coach on the App Store

Sources

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