Unit Converter
Aspartate Aminotransferase (AST/SGOT)
(Serum Glutamic-Oxaloacetic Transaminase – Hepatic & Muscle Injury Enzyme)
Synonyms
- AST
- SGOT (old name)
- Aspartate aminotransferase
- Serum glutamic-oxaloacetic transaminase
- GOT
- EC 2.6.1.1
Units of Measurement
nkat/L, µkat/L, nmol/(s•L), µmol/(s•L), U/L, IU/L, µmol/(min•L), µmol/(h•L), µmol/(h•mL)
Description
Aspartate aminotransferase (AST) is an intracellular enzyme found in:
- Liver (hepatocytes)
- Cardiac muscle
- Skeletal muscle
- Kidney
- Brain
- Red blood cells
AST is released into the bloodstream when cells are injured.
It is used to detect:
- Liver injury
- Muscle damage (myopathy, rhabdomyolysis)
- Cardiac injury (historical use before troponins)
- Toxic or ischemic hepatopathy
Physiological & Metabolic Role
AST catalyzes:
Aspartate+α−ketoglutarate↔Oxaloacetate+Glutamate\text{Aspartate} + \alpha-\text{ketoglutarate} \leftrightarrow \text{Oxaloacetate} + \text{Glutamate}Aspartate+α−ketoglutarate↔Oxaloacetate+Glutamate
Important in:
- Amino acid metabolism
- Urea cycle
- Gluconeogenesis
- Malate-aspartate shuttle (mitochondrial energy transfer)
AST exists in two isoforms:
- AST (mAST): mitochondrial
- AST (cAST): cytosolic
Mitochondrial AST rises in severe or necrotic liver damage.
Clinical Significance
Elevated AST
1. Liver Diseases
- Alcoholic hepatitis (AST/ALT ratio > 2:1)
- Viral hepatitis
- NASH / NAFLD
- Drug-induced liver injury
- Ischemic hepatitis (AST > 3000 U/L)
- Cirrhosis
2. Muscle Disorders
- Rhabdomyolysis
- Muscular dystrophies
- Myositis / polymyositis
- Intense exercise
3. Cardiac Injury (Historical)
- Myocardial infarction (not used now due to troponin)
4. Hemolysis
- RBCs contain AST → mild elevation
5. Other Causes
- Hypothyroidism
- Celiac disease
- Wilson disease
- Pancreatitis
Low AST
Not clinically significant; occasionally seen in:
- Vitamin B6 deficiency (cofactor)
- Advanced renal failure
- Chronic liver failure (loss of hepatocytes)
Reference Intervals
(Tietz 8E + IFCC 37°C method + Mayo/ARUP)
Adult Reference Range
- 10 – 40 U/L (varies by lab)
SI Units
- 0.17 – 0.67 µkat/L
Critical Patterns
- AST > 10× ULN → acute hepatitis, liver necrosis
- AST > 50× ULN → ischemic/toxic shock liver
- AST/ALT ratio > 2 → alcoholic liver disease
- AST elevated > ALT in muscle injury
Unit Meanings
| Unit | Meaning |
| nkat/L | nanokatal per liter |
| µkat/L | microkatal per liter |
| nmol/(s•L) | nanomole per second per liter |
| µmol/(s•L) | micromole per second per liter |
| U/L or IU/L | enzyme units per liter |
| µmol/(min•L) | micromole per minute per liter |
| µmol/(h•L) | micromole per hour per liter |
| µmol/(h•mL) | micromole per hour per milliliter |
Time conversions
µmol/(min•L)×60=µmol/(h•L)\text{µmol/(min•L)} \times 60 = \text{µmol/(h•L)}µmol/(min•L)×60=µmol/(h•L) µmol/(h•L)÷1000=µmol/(h•mL)\text{µmol/(h•L)} \div 1000 = \text{µmol/(h•mL)}µmol/(h•L)÷1000=µmol/(h•mL)
AST vs ALT Interpretation
| Parameter | AST | ALT |
| Tissue specificity | Liver, muscle, heart | Mostly liver |
| Alcoholic hepatitis | ↑↑ more than ALT | ↑ |
| Muscle injury | ↑↑ | Minimal ↑ |
| Cirrhosis | Mild ↑ | Mild ↑/normal |
| Viral hepatitis | Very high | Very high |
AST/ALT ratio
- 2 → Alcoholic liver disease
- <1 → Viral hepatitis, NASH
Analytical Notes
- Serum or plasma (heparin) samples acceptable.
- Avoid hemolysis → artificially increases AST.
- AST unstable → process promptly.
- Exercise may cause transient elevation.
- Pyridoxal-5-phosphate supplementation may normalize low AST in deficiency.
Clinical Pearls
- AST is less specific than ALT for hepatocellular injury.
- AST rises more than ALT in alcoholic hepatitis due to mitochondrial injury.
- Ischemic hepatitis causes massive AST elevation (often thousands).
- If AST elevated with normal ALT → investigate muscle disorders (check CK).
- AST elevation always interpreted alongside ALT, ALP, GGT.
Interesting Fact
The older name SGOT (Serum Glutamic-Oxaloacetic Transaminase) was used before the modern EC enzyme classification - still widely recognized in clinical practice.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition — Enzymes Section.
- IFCC Enzyme Standardization Guidelines - AST.
- AASLD / EASL Guidance - Liver Injury Evaluation.
- Mayo Clinic Laboratories - AST Test Catalog.
- ARUP Consult - Evaluation of Elevated Liver Enzymes.
- MedlinePlus / NIH - AST Overview.
- Hepatology Texts - Enzyme Patterns in Liver Disease.