Estimation of Serum SGOT

Table of Contents

Introduction

Estimation of Serum SGOT stands for Serum Glutamic Oxaloacetic Transaminase.
It is now commonly called AST (Aspartate Aminotransferase).
AST is an intracellular enzyme present mainly in:
liver
heart muscle
skeletal muscle
kidney
brain
red blood cells
AST catalyzes transfer of amino group between aspartate and α-ketoglutarate.
It plays an important role in amino acid metabolism and transamination reactions.
When cells are damaged, AST leaks into blood and serum level increases.
Therefore serum AST estimation is important for diagnosis of liver disease, myocardial injury, and muscle disorders.

Principle

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

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

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.
Patient Preparation:
- No specific fasting requirement; however, avoid alcohol consumption and strenuous exercise before sample collection.
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

Reagent	Composition	Concentration
R1	Tris Buffer (pH 7.8)	110 mmol/L
	L-Aspartate	340 mmol/L
	LDH	≥ 4000 U/L
	MDH	≥ 750 U/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

Increased SGOT (AST)

Increased serum AST occurs when cells containing AST are damaged and release the enzyme into blood.

Liver Diseases

AST rises in liver cell injury due to hepatocyte damage.

Seen in:

acute hepatitis
chronic hepatitis
liver cirrhosis
toxic liver injury
alcoholic liver disease

Clinical Importance

AST rises significantly in acute liver injury
In alcoholic liver disease, AST is often higher than ALT

Myocardial Infarction

AST increases after heart muscle damage.

Clinical Importance

AST begins to rise within 6–8 hours after myocardial infarction
Peak occurs at 24–36 hours
Returns to normal in 3–5 days

Skeletal Muscle Disorders

Muscle injury releases AST into blood.

Seen in:

muscular dystrophy
trauma
severe exercise
muscle inflammation

Hemolysis

Red blood cells contain AST.
Hemolysis may falsely increase serum AST.

Pancreatitis

AST may rise in pancreatic inflammation.

Renal Disease

Some kidney disorders may increase AST mildly.

Decreased AST

Decreased AST usually has little clinical significance.
Sometimes seen in severe vitamin B6 deficiency.

Diagnostic Importance

SGOT is used in liver function test (LFT).
It helps assess hepatic injury, cardiac damage, and muscle disease.
AST is always interpreted with ALT and AST/ALT ratio.

AST / ALT Ratio

Ratio helps differentiate liver diseases.

Important Pattern

AST > ALT → alcoholic liver disease
ALT > AST → viral hepatitis

MCQs

1. SGOT stands for:

A. Serum Glucose Oxidase Test
B. Serum Glutamic Oxaloacetic Transaminase
C. Serum Glutamate Oxidase Transferase
D. Serum Global Oxidative Test
Answer: B. Serum Glutamic Oxaloacetic Transaminase

2. Another name of SGOT is:

A. ALT
B. AST
C. ALP
D. ACP
Answer: B. AST

3. AST stands for:

A. Aspartate Aminotransferase
B. Alanine Transferase
C. Aspartate Transfer Protein
D. Amino Serum Test
Answer: A. Aspartate Aminotransferase

4. SGOT is mainly present in:

A. Liver
B. Heart
C. Muscle
D. All of the above
Answer: D. All of the above

5. Principle of SGOT estimation is based on:

A. GOD-POD method
B. IFCC kinetic method
C. Jaffe method
D. Biuret method
Answer: B. IFCC kinetic method

6. Primary substrate used in SGOT reaction:

A. Glucose
B. L-aspartate
C. Urea
D. Cholesterol
Answer: B. L-aspartate

7. AST transfers amino group to:

A. Pyruvate
B. α-ketoglutarate
C. Lactate
D. Citrate
Answer: B. α-ketoglutarate

8. Product formed in first reaction:

A. Pyruvate
B. Oxaloacetate
C. Lactate
D. Urea
Answer: B. Oxaloacetate

9. Coupled enzyme used:

A. LDH
B. MDH
C. Urease
D. Peroxidase
Answer: B. MDH

10. MDH stands for:

A. Malate Dehydrogenase
B. Muscle Dehydrogenase
C. Maltase Dehydrogenase
D. Mixed Dehydrogenase
Answer: A. Malate Dehydrogenase

11. Oxaloacetate converts into:

A. Malate
B. Lactate
C. Pyruvate
D. Citrate
Answer: A. Malate

12. NADH changes to:

A. NADP
B. NAD⁺
C. ATP
D. ADP
Answer: B. NAD⁺

13. Absorbance measured at:

A. 405 nm
B. 500 nm
C. 340 nm
D. 650 nm
Answer: C. 340 nm

14. SGOT estimation measures:

A. Increase in absorbance
B. Decrease in absorbance
C. Color formation
D. Turbidity
Answer: B. Decrease in absorbance

15. Preferred sample:

A. Serum
B. Whole blood
C. Urine
D. Saliva
Answer: A. Serum

16. Hemolyzed sample:

A. Preferred
B. Avoided
C. Mandatory
D. Heated
Answer: B. Avoided

17. Sample volume used:

A. 10 µL
B. 50 µL
C. 100 µL
D. 500 µL
Answer: C. 100 µL

18. Reagent volume:

A. 500 µL
B. 1000 µL
C. 200 µL
D. 2000 µL
Answer: B. 1000 µL

19. Incubation temperature:

A. 25°C
B. 30°C
C. 37°C
D. 45°C
Answer: C. 37°C

20. First incubation time:

A. 1 min
B. 10 min
C. 20 min
D. 30 sec
Answer: A. 1 min

21. Reading taken at:

A. 1, 2, 3 min
B. 5, 10 min
C. Single reading
D. End point only
Answer: A. 1, 2, 3 min

22. ΔA/min means:

A. Total absorbance
B. Change per minute
C. Standard value
D. Blank value
Answer: B. Change per minute

23. Common factor for AST:

A. 1746
B. 1000
C. 3128
D. 200
Answer: A. 1746

24. AST rises in:

A. Hepatitis
B. Myocardial infarction
C. Muscle injury
D. All of the above
Answer: D. All of the above

25. AST is part of:

A. LFT
B. Lipid profile
C. RFT
D. Thyroid profile
Answer: A. LFT

26. AST higher than ALT suggests:

A. Viral hepatitis
B. Alcoholic liver disease
C. Diabetes
D. Nephrotic syndrome
Answer: B. Alcoholic liver disease

27. ALT higher than AST suggests:

A. Viral hepatitis
B. Alcoholism
C. Muscle injury
D. Hemolysis
Answer: A. Viral hepatitis

28. AST rises in myocardial infarction after:

A. 1 hour
B. 6–8 hours
C. 24 hours
D. 48 hours
Answer: B. 6–8 hours

29. Peak AST in MI:

A. 6 h
B. 12 h
C. 24–36 h
D. 72 h
Answer: C. 24–36 h

30. Returns normal in MI:

A. 1 day
B. 3–5 days
C. 10 days
D. 2 weeks
Answer: B. 3–5 days

Short MCQs

SGOT full form = Serum Glutamic Oxaloacetic Transaminase
Modern name = AST
AST found in liver = Yes
AST found in heart = Yes
AST found in muscle = Yes
Main wavelength = 340 nm
Coupled enzyme = MDH
Coenzyme = NADH
Product = Oxaloacetate
Sample type = Serum
Method = Kinetic
AST normal male = Up to 40 U/L
AST normal female = Up to 35 U/L
Hemolysis increases AST = Yes
AST useful in LFT = Yes
AST useful in MI = Yes
AST factor common = 1746
AST decreases absorbance = Yes
AST reaction substrate = Aspartate
AST diagnostic use = Liver + Heart + Muscle