ALT (Alanine Aminotransferase)
ALT (alanine aminotransferase, formerly SGPT) is an enzyme found mainly inside liver cells. When liver cells are damaged, ALT leaks into the bloodstream. ALT is the most sensitive blood marker of liver inflammation or injury and is the first test ordered when liver disease is suspected.
Normal Range
Men: 7–55 U/L; Women: 7–45 U/L (some labs use stricter limits of <30 men, <19 women)
Reference ranges may vary slightly between laboratories. Always interpret your result in context with your doctor.
Why is ALT measured?
ALT is tested to screen for and monitor liver disease, evaluate symptoms suggesting liver damage (fatigue, jaundice, right upper abdominal pain), monitor people on medications that can affect the liver, and assess metabolic and alcohol-related liver risk.
High ALT means…
Elevated ALT indicates liver cell damage. Mild elevation (1–2× upper limit) is often non-alcoholic fatty liver disease (NAFLD). Moderate elevation (3–10×) suggests viral hepatitis, drug-induced liver injury, or alcoholic hepatitis. Very high ALT (>10×) typically reflects acute hepatitis or liver toxicity.
Low ALT means…
Low ALT is unusual and rarely clinically significant. It can occasionally suggest vitamin B6 deficiency (since B6 is a cofactor for ALT) or, in older adults, generalised muscle and liver tissue loss.
Symptoms associated with abnormal ALT
When ALT is high:
- Often no symptoms — discovered on routine blood tests
- Fatigue and reduced appetite
- Right upper abdominal discomfort
- Jaundice (yellow eyes/skin) in advanced disease
- Dark urine, pale stools
- Itchy skin
When ALT is low:
- Usually asymptomatic
How to improve your ALT
- If overweight, a 7–10% body weight loss reverses fatty liver in most cases — and typically normalises ALT.
- Limit alcohol to below 14 units per week (women) or 21 (men), with at least 2 alcohol-free days.
- Coffee (2–3 cups daily) is consistently associated with lower ALT and reduced liver disease progression.
- Avoid unnecessary supplements — many herbal preparations cause idiosyncratic liver injury.
- Recheck ALT in 4–8 weeks after lifestyle change; persistent elevation needs investigation.
Frequently asked questions about ALT
What is the difference between ALT and AST?
Both are liver enzymes, but ALT is more specific to the liver. AST is also found in heart and skeletal muscle. The AST/ALT ratio above 2:1 suggests alcoholic liver disease; below 1 is more typical of NAFLD or viral hepatitis.
Is mild ALT elevation serious?
Mild persistent elevation (50–80 U/L) is usually fatty liver and is reversible with weight loss and lifestyle change. It should not be ignored — untreated NAFLD can progress to cirrhosis over decades.
Medical Sources
This page is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider about your individual results.