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ALT

A liver enzyme that leaks into the blood when liver cells are irritated or damaged.

Typical reference range (male)9–46 U/L
Typical reference range (female)6–29 U/L

Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.

What it measures

Alanine aminotransferase is an enzyme found mainly inside liver cells, where it helps convert amino acids for energy. Small amounts in blood are normal; larger amounts appear when liver cells are injured.

Why it matters

ALT is the most liver-specific of the routine enzymes and is the main screening marker for liver inflammation, including fatty liver disease, which is very common. Many hepatologists consider values above about 33 U/L in men and 25 U/L in women worth attention even if within the lab range.

What a high result can mean

Common causes are metabolic-associated fatty liver disease, alcohol, viral hepatitis, medications and supplements (acetaminophen, statins, some antibiotics, high-dose niacin, certain herbal products), celiac disease, hemochromatosis and autoimmune hepatitis. Strenuous exercise and muscle injury can also raise ALT moderately.

What a low result can mean

Low ALT is generally not a concern. Very low values may reflect vitamin B6 deficiency, which is a cofactor for the enzyme, and are associated with frailty in older adults.

What affects the result

Avoid intense weight training for 2-3 days before testing, as muscle breakdown raises ALT and AST. Weight loss, reducing alcohol and sugar, and stopping hepatotoxic substances lower it. Compare with AST, GGT, ALP and bilirubin; an AST/ALT ratio above 2 suggests alcohol-related injury.

Units and conversion

Usually reported in U/L.

More about lab units

Also called on lab reports

ALT (SGPT), SGPT, Alanine Aminotransferase, Alanine Transaminase, ALT/SGPT, Alanine Aminotransferase (ALT)

Related tests: Liver

This page is educational and does not replace advice from a healthcare professional.