Unit Converter
Alanine Aminotransferase (ALT/SGPT)
(Serum Glutamate Pyruvate Transaminase Liver Enzyme)
Synonyms
- ALT
- SGPT (Serum Glutamate Pyruvate Transaminase)
- ALAT
- Alanine transaminase
- GPT (Glutamic Pyruvic Transaminase)
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
Alanine Aminotransferase (ALT) is an intracellular enzyme predominantly found in hepatocytes. It catalyzes the reversible transamination:
Alanine+α-ketoglutarate↔Pyruvate+Glutamate\text{Alanine} + \alpha\text{-ketoglutarate} \leftrightarrow \text{Pyruvate} + \text{Glutamate}Alanine+α-ketoglutarate↔Pyruvate+Glutamate
ALT is a sensitive marker of hepatocellular injury.
Elevated ALT indicates damage to liver cells from inflammation, necrosis, toxins, or metabolic stress.
ALT is primarily located in the cytosol of liver cells and leaks into the bloodstream when hepatocytes are damaged.
Physiological Role
- Involved in amino-acid metabolism
- Key player in the glucose–alanine cycle
- Helps convert amino acids into energy substrates
- Reflects overall hepatocyte metabolic integrity
Clinical Significance
Elevated ALT
Most commonly due to liver injury:
1. Hepatocellular Damage
- Viral hepatitis (A, B, C, E)
- Drug-induced liver injury (DILI)
- Paracetamol overdose
- Alcoholic hepatitis
- Autoimmune hepatitis
- Ischemic hepatitis (“shock liver”)
2. Metabolic Liver Disease
- Non-alcoholic fatty liver disease (NAFLD)
- NASH
- Wilson disease
- Hemochromatosis
- Alpha-1 antitrypsin deficiency
3. Systemic Causes
- Sepsis
- Thyroid disorders
- Celiac disease
- Muscle disorders (mild elevations)
Severe ALT elevations (>1000 U/L)
Seen in:
- Viral hepatitis
- Paracetamol toxicity
- Ischemic hepatitis
Low ALT
Usually not clinically significant.
Seen in:
- Severe liver failure (loss of hepatocytes)
- Vitamin B6 deficiency
- Chronic kidney disease
- Aging
Reference Intervals
Adult Reference Range
(Assay-dependent; IFCC standardized method)
- Male: 10 – 55 U/L
- Female: 7 – 45 U/L
Pediatric Values
- Infants/Children: slightly higher due to growth metabolism
(20 – 60 U/L depending on age)
SI Units Conversion
- 1 U/L = 16.67 nkat/L
- Upper limit of normal (ULN) often considered:
- Men: < 40–55 U/L
- Women: < 30–45 U/L
- Men: < 40–55 U/L
Values vary by analyzer, reagent, temperature (37°C), and lab standards.
ALT vs AST
ALT is more specific to liver than AST.
| Condition | ALT | AST |
| Viral hepatitis | ↑↑↑ | ↑↑ |
| Alcoholic liver disease | ↑ | ↑↑ (AST/ALT > 2) |
| NAFLD | ↑ | Normal or mildly ↑ |
| Muscle injury | Mild ↑ | High ↑ |
Unit Meanings
| Unit | Meaning |
| nkat/L | nanokatal per liter (SI) |
| 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)
- µmol/(h•L) ÷ 1000 = µmol/(h•mL)
Analytical Notes
- ALT measured by kinetic IFCC method at 37°C.
- Hemolysis minimally affects ALT (ALT is cytosolic).
- AST/ALT ratio helps distinguish alcoholic vs non-alcoholic liver disease.
- ALT elevation correlates with hepatic fat accumulation in NAFLD.
Clinical Pearls
- ALT > 1000 U/L strongly suggests viral hepatitis, ischemic injury, or drug-induced liver failure.
- ALT normal with high AST → alcoholic liver disease or muscle injury.
- ALT is one of the earliest enzymes to rise in acute hepatitis.
- High ALT + high GGT: think alcohol, cholestasis, or medications.
- Persistent mild ALT elevation is often NAFLD until proven otherwise.
Interesting Fact
ALT was first identified in 1955. The term SGPT (Serum Glutamate Pyruvate Transaminase) was widely used before “ALT” became the standard recommended by the IFCC.
References
- Tietz Clinical Chemistry and Molecular Diagnostics, 8th Edition - Liver Function Tests & Enzymology.
- IFCC Standardized ALT (ALAT) Enzyme Measurement Procedures.
- Mayo Clinic Laboratories - Alanine Aminotransferase (ALT) Reference Ranges.
- AASLD (American Association for the Study of Liver Diseases) - Liver Enzyme Interpretation Guidelines.
- ARUP Consult - Hepatocellular Injury Marker Interpretation.
- NIH MedlinePlus - SGPT/ALT Test.
- Pratt & Kaplan - “Evaluation of Liver Function Tests,” NEJM.