AST (SGOT) Unit Converter
AST (SGOT) Unit Converter
Convert aspartate aminotransferase between U/L, IU/L, µkat/L and nkat/L, and see why a raised AST is not always hepatic.
AST (SGOT) converter
Activity unitsAST 38 U/L
Formula and conversion factor
U/L = µkat/L × 60
- U
- 1 unit = 1 µmol of substrate converted per minute
- kat
- 1 katal = 1 mol of substrate converted per second
- ÷ 60
- the only difference between the two is per-minute versus per-second
- IU/L
- numerically identical to U/L
Worked example
AST 38 U/L
38 ÷ 60 = 0.633 µkat/L
= 633 nkat/L = 38 IU/L
Sources of a raised AST
| Source | Clue |
|---|---|
| Liver | ALT raised in proportion |
| Skeletal muscle | Creatine kinase raised, ALT normal |
| Haemolysis | Haemolysis index flagged, LDH raised |
| Cardiac | Troponin raised |
| Macro-AST | Persistent isolated elevation, well patient |
What AST measures
Aspartate aminotransferase is present in liver but also in skeletal muscle, cardiac muscle, kidney, brain and red blood cells. That distribution is the single most important thing about it: a raised AST is not, by itself, evidence of liver disease.
Within the hepatocyte, AST occupies both cytosol and mitochondria. Mitochondrial release requires more severe injury than simple membrane leak, which is why conditions that damage mitochondria — alcohol above all — raise AST disproportionately and produce the elevated AST/ALT ratio characteristic of alcohol-related liver disease.
Two non-hepatic sources catch people out regularly. Muscle is the commonest: rhabdomyolysis, myositis, seizures, intramuscular injections and even strenuous exercise raise AST with a normal or minimally raised ALT, and a creatine kinase settles it quickly. Haemolysis is the other, either in the patient or in the sample — a haemolysed specimen raises AST spuriously, and the laboratory’s haemolysis index is worth checking before investigating a liver that may be entirely normal.
Frequently asked questions
How do I convert AST from U/L to µkat/L?
Divide by 60. An AST of 38 U/L is 0.633 µkat/L. The factor is the same for every enzyme reported in units per litre.
Can a raised AST come from muscle?
Yes, commonly. AST is abundant in skeletal muscle, so exercise, rhabdomyolysis, myositis and seizures all raise it. A creatine kinase distinguishes a muscle source from a hepatic one.
Why is AST higher than ALT in alcoholic liver disease?
Alcohol damages mitochondria, releasing the mitochondrial AST isoenzyme, and depletes pyridoxal-5-phosphate which ALT synthesis needs more than AST. Both effects push the ratio above 2.
Does a haemolysed sample affect AST?
Yes. Red cells contain AST, so haemolysis in the sample raises the measured value. Check the laboratory’s haemolysis index before pursuing an unexplained elevation.
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References
- Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18–35.
- Botros M, Sikaris KA. The de Ritis ratio: the test of time. Clin Biochem Rev. 2013;34(3):117–30.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.