Biochemistry · Topic
Aminotransferases (ALT and AST) as lab tests !
ALT and AST leak into the blood when liver cells break; ALT is liver-specific, AST also comes from muscle.
Updated 2026-11-01
Key facts
- ALT (SGPT) is cytosolic and almost exclusive to the liver: it is the most specific marker of hepatocellular injury.
- AST (SGOT) is in the cytosol and mitochondria of liver, heart, skeletal muscle, kidney and red cells: it is less specific.
- AST/ALT ratio > 2 suggests alcohol-related liver disease (alcohol depletes pyridoxine and injures mitochondria); in viral hepatitis and fatty liver ALT is usually higher.
- Both use pyridoxal phosphate (vitamin B6) as a cofactor.
- Their reference range varies by laboratory, sex and age.
In detail
- What they measure: the catalytic activity of two enzymes that transfer amino groups (alanine ⇄ pyruvate; aspartate ⇄ oxaloacetate), with glutamate and α-ketoglutarate as the partner pair.
- Where they come from: ALT from the hepatocyte cytosol; AST also from mitochondria, myocardium and muscle. The blood half-life is longer for ALT (about 2 days) than for AST (under 1 day).
- Why they rise a little (under 5 times the limit): metabolic dysfunction-associated fatty liver, alcohol, chronic hepatitis B or C, drugs, haemochromatosis, coeliac disease.
- Why they rise a lot (hundreds to thousands): acute viral hepatitis, paracetamol, ischaemic hepatitis, autoimmune hepatitis, early acute biliary obstruction by a stone.
- Pitfalls: hard exercise, rhabdomyolysis and hypothyroidism raise AST (and some ALT) without liver injury; a haemolysed sample raises AST; B6 deficiency (alcohol, dialysis) can give falsely low values.
- A mild isolated rise is repeated and read against the history (alcohol, drugs, weight) before larger work-ups.
- Also called
- SGPT and SGOT, Serum transaminases, AST/ALT ratio
Clinical notes
- In ischaemic hepatitis aminotransferases reach thousands within 24–48 hours and fall fast; in viral hepatitis they fall more slowly.
- High AST with high CK suggests a muscle source, not the liver.
- In Wilson disease, a low alkaline phosphatase with high aminotransferases and haemolysis is a classic clue.
Related conditions
- Viral hepatitis
- Cirrhosis
- Myocardial Infarction (Heart Attack)
- Wilson disease
- Hereditary hemochromatosis
Related
- Alanine aminotransferase (ALT, GPT)
- Aspartate aminotransferase (AST, GOT)
- Liver function tests: reading the pattern
- Transamination and deamination
- Vitamin B6 (pyridoxal phosphate)
Test yourself
Think of the answer, then tap the question to see it.
Which aminotransferase is more liver-specific?
ALT (SGPT): it is cytosolic and almost exclusive to hepatocytes; AST is also in heart, muscle and red cells.
What does an AST/ALT ratio above 2 suggest?
Alcohol-related liver disease: alcohol depletes vitamin B6 (lowering ALT more) and injures mitochondria (releasing mitochondrial AST).
What raises aminotransferases into the thousands?
Acute viral hepatitis, paracetamol poisoning, ischaemic hepatitis and autoimmune hepatitis.
Why is a high AST not always hepatic?
AST also leaks from muscle, heart and red cells: rhabdomyolysis, hard exercise or haemolysis raise it.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: ALT Blood Test: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); AST Test: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Alanine transaminase (ALT) blood test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Aspartate aminotransferase (AST) blood test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.