Determination of Serum Cholesterol in Biochemistry

Questions and Answers

What is the purpose of the enzyme used in the cholesterol test?

To catalyze the reaction between hydrogen peroxide and 4-aminoantipyrine

To convert cholesterol into cholestenone

To measure the concentration of cholesterol in the sample

To break down cholesterol esters into cholesterol and fatty acids (correct)

What is the wavelength used to measure the absorbance of the sample in the cholesterol test?

450 nm

500 nm (correct)

600 nm

550 nm

What is the purpose of the standard used in the cholesterol test?

To calibrate the spectrophotometer

To provide a known concentration of cholesterol for comparison

To ensure the accuracy of the test

All of the above (correct)

What is the recommended temperature for incubating the samples in the cholesterol test?

37ºC Signup and view all the answers

How long should the samples be incubated in the cholesterol test?

10 minutes Signup and view all the answers

What is the conversion factor used to convert cholesterol concentration from mg/dL to mmol/L?

0.0258 Signup and view all the answers

What is the normal range for total cholesterol in adults?

Less than 200 mg/dL Signup and view all the answers

What is the recommended storage condition for cholesterol samples?

2-8ºC Signup and view all the answers

What is the primary role of HDL cholesterol in the body?

To carry cholesterol back to the liver Signup and view all the answers

What percentage of plasma cholesterol is esterified with fatty acids to form cholesterol esters?

Two-thirds Signup and view all the answers

Which type of cholesterol is referred to as 'bad cholesterol'?

LDL cholesterol Signup and view all the answers

What is the significance of determining serum cholesterol levels?

To estimate risk of cardiovascular disease Signup and view all the answers

Which of the following is NOT a risk factor for cardiovascular disease?

High physical activity levels Signup and view all the answers

Which of these is a source of cholesterol in the body?

Diet and liver production Signup and view all the answers

Study Notes

Cholesterol

Cholesterol is essential for cell membranes, hormones, and bile acids formation
It is obtained from both diet and liver production
Cholesterol is carried in the blood attached to proteins, forming lipoproteins

Types of Cholesterol

LDL cholesterol (bad cholesterol) is part of low-density lipoprotein
HDL cholesterol (good cholesterol) is part of high-density lipoprotein, helps prevent disease by carrying cholesterol away from cells to the liver for breakdown and removal

Importance of Determining Serum Cholesterol

Estimating risk of cardiovascular disease
Diagnosis and classification of lipemia
Requested for individuals with risk factors such as:
- Family history of high cholesterol or heart disease
- Being overweight or obese
- Diabetes mellitus
- High blood pressure (hypertension)
- Smoking cigarettes

Principle of the Method

Enzymatic colorimetric method used to determine total serum cholesterol level
Involves cholesterol esters, cholesterol, and fatty acids reaction
Measured spectrophotometrically at λ=500 nm and compared to a standard of known cholesterol concentration (200 mg/dL)

Test Preparation

No fasting required for a cholesterol test
Sometimes a fasting sample is required for a full lipid profile including cholesterol
Sample (serum or plasma) requirements:
- Stability of the sample for 7 days at 2-8ºC
- Freezing at –20ºC will keep samples stable for 3 months

Procedure

Assay conditions:
- Wavelength: 505 nm (500-550)
- Cuvette: 1 cm light path
- Temperature: 37ºC /15-25ºC
Reagents and sample preparation:
- Blank, standard, and sample added to cuvette
- Mix and incubate for 5 min at 37ºC or 10 min at room temperature
- Read absorbance (A) of samples and standard against the blank