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Biomarker library / Kidney and liver

ALT (alanine aminotransferase) (ALT)

Also called SGPT, alanine transaminase, liver enzyme test

ALT is an enzyme concentrated in liver cells. When liver cells are injured, ALT leaks into the blood, so the level is the standard signal of hepatocellular injury on a liver panel.

Written by the VitalDecades editorial team Reviewed by the editorial review process Updated

01  /  Reference ranges

What counts as normal

Scale in U/L. Cut points from the sources listed below.
Population Adult men (male)
Category Healthy upper limit
Range 33 or lower U/L ACG: a true healthy normal runs 29 to 33 U/L; levels above this should be assessed.
Source ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries (2017)

Effective

Population Adult women (female)
Category Healthy upper limit
Range 25 or lower U/L ACG: a true healthy normal runs 19 to 25 U/L; levels above this should be assessed.
Source ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries (2017)

Effective

Population Adult men (male)
Category Above the healthy limit: assess
Range over 33 U/L Repeat the test; evaluate for fatty liver, alcohol, viral hepatitis and medications if persistent.
Source ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries (2017)

Effective

Population Adult women (female)
Category Above the healthy limit: assess
Range over 25 U/L Repeat the test; evaluate for fatty liver, alcohol, viral hepatitis and medications if persistent.
Source ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries (2017)

Effective

Normal vs optimal

Many labs print upper limits of 40 U/L or higher, historic ranges built from populations that included undiagnosed fatty liver. The ACG's healthy-population upper limit (33 male, 25 female) is the better yardstick for a screening result; a persistently higher value warrants evaluation even if the report is not flagged.

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02  /  Why it matters

What the number tells you

The most common reason for a high ALT today is metabolic dysfunction-associated fatty liver disease, which travels with the same weight, glucose and lipid numbers this site tracks. The ACG guideline notes that an elevated ALT is associated with increased liver-related mortality, and, importantly, that a truly healthy normal is lower than many lab ranges print: 29 to 33 U/L for males and 19 to 25 U/L for females, with levels above that deserving assessment.

03  /  In practice

Testing and what moves it

When it is tested

  • On a routine comprehensive metabolic panel, or when fatty liver, alcohol, viral hepatitis or a new medication is in question.
  • Confirm an unexpected elevation with a repeat test; ALT moves with recent illness and vigorous exercise.
  • The evaluation of a persistent elevation (per ACG) covers viral hepatitis, fatty liver, alcohol, medications, iron overload and autoimmune causes.

What raises it

  • Fatty liver disease, alcohol, viral hepatitis A/B/C, medications and supplements (acetaminophen in excess, some statin idiosyncrasy, bodybuilding supplements), hemochromatosis.
  • Transiently: strenuous exercise, muscle injury.

What lowers it

  • Weight loss and treating the underlying cause; ALT falling toward the healthy range is a treatment signal in fatty liver.
  • A very low ALT has little clinical meaning.

04  /  Related

Read next

Hemoglobin A1C A1CTriglycerides TGeGFR (estimated glomerular filtration rate) eGFR

Frequently asked questions

My lab says ALT under 40 is normal. Why do you print 33?

Lab ranges were historically built from populations that included people with undiagnosed fatty liver. The ACG guideline states a true healthy normal ALT is 29 to 33 U/L for males and 19 to 25 U/L for females, and that levels above this should be assessed.

What is the most common cause of a mildly high ALT?

Fatty liver disease, which tracks with weight, waist size, triglycerides and A1C. Alcohol, medications and viral hepatitis are the other front-line considerations in the ACG evaluation.

Can exercise raise ALT?

Yes, hard training and muscle injury can bump ALT (and AST more) for days. Re-test after a few days without strenuous exercise before chasing a mild elevation.