ALT (Alanine Aminotransferase)

What is ALT?

ALT (alanine aminotransferase), also known as SGPT, is an enzyme found primarily in liver cells. Unlike AST, which appears in multiple organs, ALT is highly specific to the liver.

When liver cells are damaged or inflamed, ALT leaks into the bloodstream. This makes ALT the most sensitive and specific blood test for detecting liver injury.

Even mild elevations can indicate early liver problems, often before symptoms appear.

Normal Ranges

Group	ALT Level
Adult men	7–56 U/L
Adult women	7–45 U/L

Some experts argue that optimal ALT should be even lower — below 30 U/L for men and 19 U/L for women — to catch subtle liver stress.

Why It Matters

Early Liver Disease Detection

ALT elevations often appear before symptoms develop. Catching fatty liver or hepatitis early allows for intervention before significant damage occurs.

Fatty Liver Screening

Non-alcoholic fatty liver disease (NAFLD) affects roughly 25% of adults. Elevated ALT is often the first sign, even in people who feel healthy.

Medication Safety

Regular ALT monitoring protects people taking medications that can stress the liver, including statins, certain antibiotics, and pain medications.

What Causes High ALT

Common Causes

Fatty liver disease — The most common cause today
Excessive alcohol — Even moderate drinking can elevate ALT
Medications — Acetaminophen, statins, antibiotics
Viral hepatitis — Hepatitis B and C

Less Common Causes

Autoimmune hepatitis
Celiac disease
Thyroid disorders
Muscle injury (rare, as ALT is liver-specific)

ALT and the AST/ALT Ratio

Comparing ALT to AST helps diagnose specific conditions:

ALT higher than AST: Suggests fatty liver or viral hepatitis
AST higher than ALT: Suggests alcoholic liver disease or cirrhosis

What Affects ALT

Alcohol — Even moderate intake raises levels
Obesity — Strongly linked to fatty liver
High-fructose diet — Contributes to liver fat
Intense exercise — Can cause temporary elevation
Supplements — Some herbal products stress the liver

How to Improve ALT

If your ALT is elevated due to lifestyle factors:

Reduce or eliminate alcohol
Lose excess weight gradually
Limit fructose and refined carbohydrates
Exercise regularly
Review supplements with your doctor

How Often to Test

Routine checkups: Often included in comprehensive panels
Taking liver-affecting medications: Every 3–6 months
Elevated levels: Repeat in 2–4 weeks to confirm