SGOT

Introduction

1. SGOT is an enzyme that catalyzes the reversible transfer of an amino group between aspartate and α-ketoglutarate to form oxaloacetate and glutamate.
2. Under normal physiological conditions, SGOT is present primarily within cells, with only a small amount circulating in the blood.
3. When cells are damaged, SGOT is released into the bloodstream, making its measurement an important biomarker for tissue injury.

Methods

 IFCC methods

 

---

Principles

The SGOT assay relies on the enzymatic transfer of an amino group between aspartate and α-ketoglutarate to form oxaloacetate and glutamate.

Primary Reaction:

Aspartate + α-Ketoglutarate →                 SGOT                   Oxaloacetate + Glutamate

The oxaloacetate produced in this reaction is further used in a coupled reaction involving NADH, which is oxidized to NAD⁺ in the presence of malate dehydrogenase (MDH):

Coupled Reaction:

Oxaloacetate + NADH + H⁺  →                  MDH                    Malate + NAD⁺

The decrease in absorbance at 340 nm, due to the oxidation of NADH to NAD⁺, is directly proportional to the SGOT activity in the sample.

 

---

Sample Collection and Handling

1. Sample Type:
   • Serum or plasma is preferred.
   • Heparinized plasma is acceptable, but EDTA, citrate, or fluoride anticoagulants should be avoided as they may interfere with the enzymatic reactions.
2. Patient Preparation:
   • No specific fasting requirement; however, avoid alcohol consumption and strenuous exercise before sample collection.
3. Sample Storage:
   • The serum should be analyzed as soon as possible.
   • If delayed, store samples at 2–8°C for up to 48 hours or freeze at -20°C for longer storage.

 

---

Reagents

R1

Tris Buffer (pH 7.8)                                        110 mmol/l

L-Aspartate                                                       340 mmol/l

LDH                                                                   ≥4000 U/l

MDH                                                                 ≥750U/l

R2

CAPSO                                                              20 mmol/l

2-Oxoglutarate                                                85 mmol/l

NADH                                                              1.05 mmol/l

 

---

Procedure

Reagent 1 (buffer)	1.000 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). 340 nm

 

---

Calculation

The SGOT activity is calculated based on the rate of change in absorbance (ΔA) per minute:

SGOT Activity (U/L) = ΔA × Vt × 1000/ϵ × d × Vs​

Where:

• ΔA : Change in absorbance per minute.
• Vt​: Total reaction volume (mL).
• Vs : Sample volume (mL).
• ϵ: Molar absorptivity of NADH at 340 nm (6.22 x 10³ L/mol/cm).
• d: Path length of the cuvette (cm).

 

---

Normal Range

The reference range for SGOT levels may vary slightly between laboratories but typically falls within:

• Adults: 8–40 U/L
• Children: 10–50 U/L
• Neonates: Up to 80 U/L

---

Clinical Significance

Elevated SGOT Levels:

1. Liver Disease:
   • Hepatitis, liver cirrhosis, fatty liver disease, and hepatocellular carcinoma.
   • SGOT is often elevated with serum glutamic-pyruvic transaminase (SGPT/ALT).
2. Myocardial Infarction:
   • SGOT rises within 6–12 hours of myocardial infarction, peaks at 24–36 hours, and returns to normal in 3–5 days.
3. Skeletal Muscle Disorders:
   • Muscular dystrophy, rhabdomyolysis, and trauma.
4. Other Conditions:
   • Acute pancreatitis, hemolytic anemia, and drug-induced toxicity (e.g., alcohol, statins, or paracetamol overdose).

Low SGOT Levels:

• Rarely of clinical significance but may occur in conditions like vitamin B6 deficiency, as SGOT requires pyridoxal phosphate as a coenzyme.