Quick Guide: Aminotransferase, alanine (ALT) Blood Test
What it is: An ALT (alanine aminotransferase) test measures the level of ALT, an enzyme found mainly in the liver, in a blood sample.
Why it's ordered: Ordered to evaluate liver health, usually as part of a liver panel or comprehensive metabolic panel, when a provider suspects liver damage from hepatitis, fatty liver disease, medication effects, or alcohol use, or to monitor a known liver condition.
What it detects: ALT leaks into the blood when liver cells are damaged, so elevated levels point to liver injury. Because ALT is more concentrated in the liver than AST, it's considered a fairly specific marker of liver (rather than muscle or heart) damage.
Collection & prep: A standard blood draw from a vein in the arm. ALT is rarely tested alone; when it's part of a larger panel, fasting may be requested, and certain medications can affect results.
Results:
High – typically above 45 IU/L in adults; suggests liver cell damage from hepatitis, fatty liver disease, or medication/alcohol effects
Normal – roughly 0–45 IU/L, though ranges vary by lab
Possible complications of liver damage: A single elevated ALT doesn't diagnose a specific disease — it's usually interpreted alongside AST, ALP, and GGT to narrow down the cause, and repeat testing can track whether a liver condition is progressing or resolving.
Statements made in the Clinical Manual have not been evaluated by the FDA. The products mentioned are not intended to diagnose, treat, cure or prevent any disease.
