You ran a half marathon Saturday, got blood drawn Monday, and now AST is 80. Your doctor mentioned the liver. The liver is fine. Your quads are not.
AST (aspartate aminotransferase, called SGOT on older reports) lives in liver cells, but also in muscle, heart, kidney, and red blood cells. That's the whole reason it gets misread. A high AST with a normal ALT is almost never the liver. It's the workout, the bruise, the hemolyzed sample tube.
The number that actually matters is AST paired with ALT, and especially the ratio between them. Most mild AST elevations are fatty liver or alcohol and walk back with a few months of lifestyle change. The readings that demand a phone call today are the dramatic ones, ten times the upper limit or more, which point at acute hepatitis, ischemia, or rhabdomyolysis.
What AST measures
AST is an enzyme that helps shuffle amino acids around inside cells. When those cells get damaged, AST leaks into the blood. The catch: the cells live in too many places. Liver, skeletal muscle, heart, kidney, red blood cells. So an isolated high AST without a high ALT is often a muscle story, not a liver story.
Read AST alongside ALT. Almost never alone.
- AST/ALT ratio above 2 with elevated values: classic for alcohol-related liver disease, advanced fibrosis (cirrhosis), or muscle injury.
- AST/ALT ratio below 1: typical for non-alcoholic fatty liver disease (MASLD) and most viral hepatitis.
- AST and ALT both very high (>10× upper limit) with similar magnitudes: acute hepatitis, drug-induced liver injury, ischemic liver injury.
AST reference range
| Grupo demográfico | Bajo | Alto | Unidad |
|---|---|---|---|
| Normal | 8 | 48 | U/L |
| Mildly elevated | 49 | 150 | U/L |
| Moderately elevated | 151 | 500 | U/L |
| Markedly elevated | 500 | 5000 | U/L |
- Normal: 8–48 U/L for most labs.
- Mildly elevated: up to 3× upper limit (typically up to ~150 U/L).
- Moderately elevated: 3–10× upper limit.
- Markedly elevated: above 10× upper limit (typically above 500 U/L).
- Above 1,000 U/L: uncommon and serious. Usually viral hepatitis, drug-induced liver injury, ischemic hepatitis, autoimmune hepatitis, or severe rhabdomyolysis.
What high AST means
Same suspects as ALT, plus muscle:
- MASLD (fatty liver): most common; usually mild, often AST < ALT.
- Alcohol-related liver disease: classic AST > ALT pattern (ratio above 2).
- Medications: statins (mild), acetaminophen (especially overdose), antibiotics (amoxicillin-clavulanate, isoniazid), antiepileptics, methotrexate, herbal supplements.
- Viral hepatitis: A through E. Acute hepatitis can produce dramatic elevations.
- Autoimmune hepatitis: uncommon but treatable.
- Hereditary conditions: hemochromatosis, Wilson's disease, alpha-1 antitrypsin deficiency.
- Muscle injury: strenuous exercise (especially in the 24–72 hours before the test), rhabdomyolysis, polymyositis, statin-related myopathy. Check creatine kinase (CK) when AST is high but ALT is normal.
- Heart and kidney injury: modestly raise AST.
- Hemolysis: including hemolyzed sample tubes (artifactual elevation).
- Celiac disease, thyroid disease: sometimes raise both AST and ALT modestly.
What to do first: repeat the panel in 2 to 4 weeks. Roughly half of mild elevations resolve on their own. While you're at it, add CK (rules out muscle), TSH, ferritin, and hepatitis B/C serology.
Low AST
Low AST rarely matters. A very low value can hint at vitamin B6 deficiency (B6 is a cofactor for the enzyme) or, in older adults, weakly track with frailty. No intervention needed.
Reading AST in context
The AST/ALT ratio (the De Ritis ratio, if you want the textbook name) is the one piece of information AST adds beyond ALT:
- Ratio < 1: typical for fatty liver and most viral hepatitis.
- Ratio 1–2: nonspecific; consider broader workup.
- Ratio > 2 with mild elevation: alcohol-related liver injury until proven otherwise.
- Ratio > 2 with normal alcohol use: consider advanced fibrosis or cirrhosis. The FIB-4 score formalizes this signal alongside age and platelets.
AST moves fast. Alcohol cessation drops it within 1 to 2 weeks. Weight loss starts to lower it in 4 to 6. Treating the underlying cause shows results inside 8 to 12.
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When AST warrants action
- AST above 3× upper limit on confirmed retest: focused workup for cause.
- AST above 10× upper limit: urgent evaluation: acute hepatitis, drug injury, ischemic liver, severe rhabdomyolysis.
- AST above 1,000 U/L: emergency.
- AST/ALT ratio above 2 with mild elevations: review alcohol use; if alcohol is genuinely minimal, consider fibrosis workup.
- High AST with normal ALT: almost certainly muscle, not liver. Order CK.
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Tests that complete the picture
- ALT: paired with AST; the ratio drives interpretation.
- Alkaline phosphatase (ALP) and GGT: bile flow / cholestasis.
- Bilirubin (total and direct): liver excretory function.
- Albumin and INR: liver synthetic function.
- Creatine kinase (CK): confirms muscle source when AST is high but ALT is normal.
- Hepatitis B surface antigen, Hepatitis C antibody: viral hepatitis screen.
- Iron studies, ceruloplasmin, alpha-1 antitrypsin: hereditary causes.
- Platelets: drop in advanced cirrhosis; component of FIB-4.