Introduction
- Serum Glutamate Pyruvate Transaminase (SGPT), also known as Alanine Aminotransferase (ALT), is a liver enzyme primarily involved in amino acid metabolism.
- It is commonly used as a biomarker to assess liver function.
- Elevated SGPT levels indicate liver cell damage, as the enzyme is released into the bloodstream when hepatocytes are injured.
- It is also valuable in diagnosing conditions like hepatitis, fatty liver disease, and liver cirrhosis.
Principle
L-Alanine + 2-oxoglutarate ALT/GPT Pyruvate + L-Glutamate
Pyruvate + NADH LDH L-Lactate + NAD+
Sample pyruvate + NADH LDH L-Lactate + NAD
In the presence of SGPT, alanine transfers its amino group to α-ketoglutarate, producing pyruvate and glutamate. Pyruvate is then reduced to lactate by lactate dehydrogenase (LDH) with the simultaneous oxidation of NADH to NAD⁺. The rate of decrease in NADH absorbance at 340 nm is proportional to SGPT activity.
Methods
IFCC Method
Samples
- Sample Type: Serum or plasma (collected in heparinized tubes).
- Sample Volume: ~0.5 mL.
- Storage: Samples should be analyzed within 24 hours. If not processed immediately, store at 2–8°C for up to 48 hours. Prolonged storage may affect enzyme activity.
Reagents
R1
Tris Buffer (pH 7.5) 137.5 mmol/l
L-Alanine 709 mmol/l
LDH (microbial) ≥ 2000 U/l
R2
CAPSO 20 mmol/l
2-oxoglutarate 85 mmol/l
NADH 1.05 mmol/l
Reagent Preparation: Follow the manufacturer’s instructions for reagent preparation and stability.
Procedure
| Reagent 1 (buffer) | 1 ml |
| Sample | 0.100 ml |
|
Mix and incubate for 5 min. at 37°C. Then add: |
|
| Reagent 2 (substrate) | 0.250 ml |
Mix, incubate 1 min. At 37°C, measure the calibrator’s initial absorbance and sample against the reagent blank. Measure the absorbance change exactly after 1, 2, and 3 min. Calculate a 1-minute absorbance change (ΔA/min).
Calculation
SGPT activity is expressed in units per liter (U/L). The calculation is based on the change in absorbance per minute (ΔA/min):
SGPT (U/L) = ΔA/min × Vt × 1000/ϵ × d × Vs
Where:
-
- Vt: Total reaction volume (mL)
- Vs: Sample volume (mL)
- ϵ: Molar extinction coefficient of NADH (6.22 L/mmol/cm)
- d: Path length of cuvette (cm)
Normal Range
- Adults: 7–56 U/L
- Children: Slightly higher values due to active growth.
Note: Normal ranges may vary depending on the laboratory and assay method.
Clinical Significance
- Elevated SGPT Levels:
- Acute liver diseases (e.g., hepatitis, toxic liver injury)
- Chronic liver diseases (e.g., cirrhosis, fatty liver)
- Alcohol or drug-induced hepatotoxicity
- Muscle disorders (mild elevation due to muscle damage)
- Decreased SGPT Levels:
- Severe liver damage with significant loss of functional hepatocytes.