Biochem prac 1: Liver function tests

Metabolic Function of Liver

Metabolizes or breaks down nutrients from food to produce energy when needed.

Excretory Function of Liver

Produces bile, a compound needed to digest fat and absorb vitamins A, D, E, and K.

Synthetic Function of Liver

Produces most proteins needed by the body; produces most substances that regulate blood clotting.

Detoxification Function of Liver

Removes potentially toxic byproducts of certain medications; helps the body fight infection by removing bacteria from the blood.

Storage Function of Liver

Prevents shortages of nutrients by storing vitamins, minerals, and sugar.

Reasons to Test Liver Function

1. Screening for liver disease (such as hepatitis).

2. Measuring severity of disease (especially assessing degree of liver scarring).

3. Monitoring disease progression and determining treatment effectiveness.

4. Monitoring possible side effects of medications.

Clinical Lab Tests for Integrity of Liver Cells

AST (SGOT) and ALT (SGPT).

Clinical Lab Tests for Excretory Function

Bilirubin (Total, Direct, Indirect), Alkaline Phosphatase (ALP), and Gamma GT (GGT).

Clinical Lab Tests for Synthetic Function

Serum Albumin and Prothrombin time (also Total Protein and Globulin).

Components of LFT Profile

Total Protein, Albumin, Globulin, Bilirubin (Total, Direct, Indirect), and Liver Enzymes (SGOT/AST, SGPT/ALT, ALP, GGT).

Serum Transaminases (Aminotransferases) Definition

Among the most sensitive and widely used liver enzymes. They catalyze the interconversion of amino acids and ketoacids by transfer of an amino group.

SGOT Full Name & Alias

Serum Glutamic Oxaloacetic Transaminase, also known as Aspartate Aminotransferase (AST).

SGPT Full Name & Alias

Serum Glutamic Pyruvic Transaminase, also known as Alanine Aminotransferase (ALT).

Reaction Catalyzed by ALT

Alanine + α-Ketoglutarate ↔ Pyruvate + Glutamate

Reaction Catalyzed by AST

Aspartate + α-Ketoglutarate ↔ Oxaloacetate + Glutamate

ALT Activity Assay Principle (Kinetic Method)

Step 1: L-alanine + oxoglutarate -- (ALT/GPT) --> pyruvate + L-glutamate.

Step 2: Pyruvate + NADH + H+ -- (LDH) --> L-Lactate + NAD+ + H2O.

Reduced coenzyme (NADH) consumption is proportional to ALT activity.

AST Activity Assay Principle (Kinetic Method)

Step 1: α-ketoglutarate + L-aspartate --(AST/GOT)--> L-glutamate + oxaloacetate.

Step 2: Oxaloacetate + NADH + H+ --(MDH)--> L-Malate + NAD+ + H2O. Reduced coenzyme (NADH) consumption is proportional to AST activity.

Transaminase Kinetic Assay Parameters

Wavelength: 365 nm.

Incubation temperature: Room temperature.

Zero adjustment: Against air.

Transaminase Assay Pipetting Volumes (Macro vs. Semi-micro)

Macro: Specimen = 200 µL, Working solution = 2.0 mL.

Semi-micro: Specimen = 100 µL, Working solution = 1.0 mL.

Transaminase Assay Procedure Steps & Measurement

Mix, read initial absorbance after 60 seconds, and start timer simultaneously. Read again after 1, 2, and 3 minutes to determine mean absorbance change per minute (ΔA/min).

Transaminase Calculation Formula

U/L = 3235 × ΔA =

Serum Albumin Properties & Production

Most abundant plasma protein in humans (accounts for about 60% of total serum protein). Produced ONLY in the liver.

Colorimetric Estimation of Albumin Principle

At pH 4.3, albumin is sufficiently cationic to bind the anionic indicator dye Bromocresol Green (BCG) forming a blue-green colored complex.

Albumin Colorimetric Reaction Formula

Albumin + BCG --(pH 4.3)--> Albumin-BCG Complex (intensity of blue-green color is directly proportional to albumin concentration).

Albumin Assay Pipetting Procedure

Sample: Serum or plasma.

Blank: R2 2.5 mL.

Standard: R2 2.5 mL + Standard 10 µL. Sample: R2 2.5 mL + Sample 10 µL.

Albumin Assay Incubation & Reading

Mix and incubate for 5 min at 20-25°C. Measure absorbance of sample and standard against a blank at wavelength 630 nm.

Albumin Concentration Calculation Formula

Albumin concentration (g/dL) = (A_specimen / A_standard) × 4

AST (SGOT) Normal Reference Value

5 to 40 U/L

ALT (SGPT) Normal Reference Value

7 to 56 U/L

Clinical Significance of Transaminase Reference Ranges

Ranges may differ from lab to lab depending on technique and protocols. Determination is extremely useful in assessing severity and prognosis of parenchymal liver diseases, especially acute hepatitis (where highest values in thousands of units are seen).

AST (SGOT) Tissue Distribution & Diagnostic Implications

Found in many tissues including liver, heart, muscle, kidney, and brain (NOT specific to liver). Released when any of these tissues are injured/damaged; elevated in liver diseases, myocardial infarction, and muscle disease.

ALT (SGPT) Tissue Distribution & Diagnostic Implications

Found primarily in hepatocytes. Released into the bloodstream as a result of liver injury. Serves as a SPECIFIC indicator of liver status. Elevated in primary liver diseases (cirrhosis, carcinoma, viral/toxic hepatitis, obstructive jaundice).

Causes of Mild to Moderate AST and ALT Elevations

1. Fatty liver (most frequently due to alcohol abuse).

2. Chronic hepatitis B and C.

3. Medications (Pain relievers: aspirin, ibuprofen, diclofenac; Antibiotics: tetracyclines, sulfonamides).

Serum Albumin Normal Reference Value

3.5 to 5 g/dL

Diagnostic Importance of Low Serum Albumin

Lower than normal levels strongly suggest chronic liver disease (though many non-liver conditions can also cause low levels).

Causes of Hypoalbuminemia (Intake/Absorption)

Malnutrition (starvation) and malabsorption (Crohn's disease).

Causes of Hypoalbuminemia (Synthesis)

Chronic liver disease.

Causes of Hypoalbuminemia (Catabolism)

Tissue damage (severe burns) or chronic infection / prolonged fever / inflammation.

Causes of Hypoalbuminemia (Loss)

Nephrotic syndrome.

Pathophysiology of Edema and Ascites in Hypoalbuminemia

Low plasma osmotic pressure caused by hypoalbuminemia allows water to move out of blood capillaries into tissues, leading to edema and ascites.