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ALT (alanine transaminase)
A liver enzyme that leaks into the blood when liver cells are injured.
Other names: Alanine aminotransferaseSection: Blood chemistry
Updated: August 29, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortA common adult reference range is 4–36 U/L. Higher values usually mean liver cell injury; low values are uncommon.
Reference ranges
Group
Reference range
Adults
4–36 U/L
Reference ranges vary slightly between laboratories, and some labs use different measurement methods. The range printed on your own report is the one that applies to your result.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
ALT (alanine aminotransferase) is an enzyme — a protein that drives a specific chemical reaction — found in high concentrations inside liver cells. When liver cells are injured, ALT is released into the bloodstream, and the level measured in a blood sample rises. The result is reported as enzyme activity in units per liter (U/L).
The test is rarely interpreted alone. It is usually measured together with other liver blood tests such as AST, alkaline phosphatase, and bilirubin, and the provider compares the whole set to judge liver health and decide whether more testing is needed. An isolated mild rise, with everything else normal, is read differently from a rise across several liver tests.
Blood is drawn from a vein, usually on the inside of the elbow, and the draw takes a few minutes. No special preparation is needed. Because many medicines and dietary supplements can shift the result, it helps to arrive with a full list of what you take.
A single ALT value is a signal, not a diagnosis. Providers look at how far the value is above the reference range, whether it is rising or falling over time, and what the other liver tests show before deciding what the number means for a particular person.
When it is high
HepatitisA swollen and inflamed liver releases ALT from injured cells. Hepatitis is one of the classic reasons for a raised ALT.
CirrhosisScarring of the liver damages liver tissue over time, and ALT leaks from the affected cells.
Fatty liver diseaseToo much fat stored in the liver is a frequent cause of a mild, persistent ALT rise.
Alcohol and liver-toxic medicinesSubstances that are toxic to the liver — including alcohol and medicines such as acetaminophen — can injure liver cells and raise ALT. Certain cholesterol and pain medicines are also on this list.
Reduced blood flow to the liverWhen the liver does not get enough blood (liver ischemia), its cells are injured and ALT rises.
Other causesLiver tumors or cancer, mononucleosis, pancreatitis, and too much iron in the body (hemochromatosis) can also raise ALT.
When it is low
Vitamin B6 deficiencyA lower-than-usual ALT is uncommon, but too little vitamin B6 in the body is one of the reasons a low value can appear.
Chronic kidney diseaseLong-term kidney disease is the other situation in which a low ALT level may be seen.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Intense exercisePhase of the menstrual cycleCertain medicines and dietary supplementsAge, sex, and body weight
How to prepare
No special preparation is needed. Tell your provider about all medicines and dietary supplements you take, because some of them can shift the result.
When a retest makes sense
An unexpected value is usually confirmed with a repeat test and read together with AST, alkaline phosphatase, and bilirubin. A persistently high ALT leads to a search for the source of liver injury.
Who usually reviews this result
A result outside the reference range is usually reviewed by: your GP or primary care doctor; a gastroenterologist or hepatologist if liver disease is suspected. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: ALTAlanine aminotransferaseAlanine transaminaseSGPTGPTSerum glutamic-pyruvic transaminase
Units
Measured in: U/L
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
Yes. Intense exercise is one of the factors that can shift an ALT result, along with age, sex, body weight, certain medicines and dietary supplements, and the phase of the menstrual cycle. Mention a recent hard training block to your provider.
How is ALT different from AST?
Both enzymes rise when the liver is injured, but AST is also found in the heart and muscles, while ALT is concentrated in the liver. Read together, the pair helps separate liver injury from other tissue damage.
Does a slightly high ALT need treatment?
Not necessarily. A result outside the reference range does not always mean there is a medical condition that needs treatment. The provider weighs the size of the rise, the trend over time, and the other liver tests before deciding.
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