Laboratory Techniques: Measuring Absorbance

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Questions and Answers

What is the primary function of lipoproteins in the body?

To deliver fuel to peripheral cells

Which of the following conditions is associated with decreased cholesterol levels?

Severe hepatocellular disease

What is the characteristic shape of lipoproteins?

Spherical

Which type of hyperlipoproteinemia is associated with severe hepatocellular disease?

Type III Signup and view all the answers

What is the component of lipoproteins that is responsible for delivering fuel to peripheral cells?

Triglycerides Signup and view all the answers

Nephrotic syndrome is characterized by?

Increased cholesterol levels Signup and view all the answers

What is the method used to separate lipoproteins into fractions?

Ultracentrifugation Signup and view all the answers

Which of the following conditions is associated with increased cholesterol levels?

Nephrotic syndrome Signup and view all the answers

What is the wavelength used in the assay?

500 nm Signup and view all the answers

What is the conversion factor to convert mg/dL to mmol/L?

0.0259 Signup and view all the answers

What is the incubation temperature and time for the assay?

37°C for 5 minutes Signup and view all the answers

What is the optical path used in the assay?

1 cm Signup and view all the answers

What is the formula to calculate the concentration of the unknown sample?

Concentration unknown = Concentration std x Abs unknown / Abs std Signup and view all the answers

What is the purpose of the reagent blank?

To measure the absorbance of the reagent Signup and view all the answers

What is the primary function of HDL in reverse cholesterol transport?

Removing excess cholesterol from peripheral cells Signup and view all the answers

What is the major protein component of HDL?

Apolipoprotein A-1 Signup and view all the answers

According to the American National Cholesterol Education Program, what is the HDL-C level that indicates high risk for developing coronary artery disease?

< 40 mg/dL Signup and view all the answers

What is the name of the process by which HDL removes excess cholesterol from peripheral cells?

Reverse cholesterol transport Signup and view all the answers

Which of the following lipoproteins is NOT synthesized in the liver and intestine?

Chylomicrons Signup and view all the answers

What is the function of discoid HDL?

More active in cholesterol transport Signup and view all the answers

What is the unit of measurement for HDL-C levels?

mmol/L Signup and view all the answers

What is the primary site of HDL synthesis?

Liver and intestine Signup and view all the answers

What is the significance of HDL-C levels in the context of coronary artery disease?

Low HDL-C levels are associated with high risk of CAD Signup and view all the answers

What is the name of the classification system used to determine the risk of developing coronary artery disease based on HDL-C levels?

American National Cholesterol Education Program Signup and view all the answers

Study Notes

Assay Requirements

Wavelength: 500 nm
Optical path: 1 cm
Temperature: 37°C
Measurement: Read against reagent blank (only one reagent blank per series is required)

Computations

Formula: Concentration CN = concentration std x Abs CN / Absstd
Compute for cholesterol concentration of patient's sample in mg/dL and mmol/L
Concentration of standard: 100 mg/dL
Conversion factor: mg/dL x 0.0259 = mmol/L

Clinical Significance

Increased Cholesterol:
- Associated with hyperlipoproteinemia types II, III, V
- Biliary cirrhosis
- Nephrotic syndrome
- Poorly controlled diabetic mellitus
- Alcoholism
- Primary hypothyroidism
Decreased Cholesterol:
- Severe hepatocellular disease
- Malnutrition
- Severe burns
- Hyperthyroidism
- Malabsorption syndrome

Lipoproteins

Spherical in shape, ranging in size from 10 to 1,200 nm
Composed of both proteins and lipids (apolipoproteins)
Main role: delivery of fuel to peripheral cells
Separated into fractions through ultracentrifugation
Types: Chylomicrons, HDL, LDL, VLDL

HDL (High-Density Lipoprotein)

Smallest and most dense lipoprotein particle
Synthesized in the liver and intestine
Two forms: discoid (nascent, more active) and spherical (formed when discoid binds additional lipids)
Removes excess cholesterol from peripheral cells (reverse cholesterol transport) > “good cholesterol”
Apolipoprotein A-1: major protein component
Index used to determine amount of HDL-C

HDL-C Determination

American National Cholesterol Education Program Risk Classification for Developing Coronary Artery Disease
HDL-C Risk Classification:
- High Risk: < 40 mg/dL (< 1.03 mmol/L)
- Low Risk: ≥ 60 mg/dL (≥ 1.55 mmol/L)

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