2. Decreased values are associated with

 a. Increased risk of coronary heart disease when

HDL—Cholesterol is less than 45 mg/dL in men

and less men 55 mg/dL in women.

 b. Inheritance and chronic physical inactivity (25–35

mg/dL). Long level distance runners have higher

levels of HDL.

3. Levels can be either high or low in primary biliary

cirrhosis, chronic hepatitis, or alcoholism.

Interfering Factors

1. Decreased HDL is associated with smokers.

2. Increased HDL is associated with moderate intake of

alcohol.

3. Iodine contrast substances interfere with test results.

4. Recent weight gains or losses can interfere with the

test results.

Patient Preparation

1. Overnight fasting is required. Water is permitted.

2. If possible, all medication should be withheld for 24

to 48 hours before testing—confer with attending

physician regarding this.

3. Ask patient if there has been any drastic change in

weight in last few weeks before testing.

Patient Aftercare

Person with decreased HDL can be counseled to take

measures to increase levels by losing weight, cutting down

on calories consumption, eating less red meat, and taking

lecithin supplements. Moderate alcohol consumption is

believed by some to be a factor in increased HDL.

Cholesterol: LDL and VLDL

Very low density lipoproteins (VLDL) and low-density

lipoproteins (LDL).

Normal Values

VLDL cholesterol: 25–50%

LDL cholesterol: 62–185 mg/dL.

VLDL is a major carrier of triglyceride (60-70%

triglyceride, 10–15% cholesterol). Degradation of VLDL

leads to a major source of LDL. Circulating fatty acids are

vitalized by the liver to form triglycerides that are packaged

with apoprotein and cholesterol and exported into the

blood as very low density lipoproteins.

LDLs are the cholesterol rich remnants of the lipid

transport vehicle, VLDL. Since, LDL has a longer half-life

(3–4 days) than its precursor, VLDL, LDL is more prevalent

in the blood. It is finally catabolized in the liver and

possibly in nonhepatic cells as well.

LDL-Cholesterol Fully Enzymatic, Colorimetric Test

(Courtesy: Randox)

Principle

Low-density lipoproteins (LDL) are precipitated by heparin

at their isoelectric point (pH 5.04). After centrifugation the

high-density lipoproteins (HDL) and the very low-density

lipoproteins (VLDL) remain in the supernatant. These can

then be determined by enzymatic methods.

LDL-cholesterol = Total cholesterol–cholesterol in the

supernatent.

Sample

Serum

Reagents

Contents Initial Concentration of Solution

1. Precipitation Reagent

 Heparin 50,000 IU/L

 Sodium citrate 0.064 mol/L, pH 5.04.

Preparation of Reagents

1. Precipitation reagent

 Ready for use

 Stable up to expiry date when stored at + 2 to + 8°C.

2. Reagent solution for cholesterol determination.

Procedure

Wavelength 500 nm Hg 546

Cuvette 1 cm light path

488 Concise Book of Medical Laboratory Technology: Methods and Interpretations Temperature + 20 to + 25°C, 37°C

Pipette into centrifuge tube

Serum 100 µL

Precipitation reagent (1) 1000 µL

Mix well, have to stand for 10 minutes at + 15 to

+ 25°C and centrifuge for 15 minutes at approx. 4000

rpm. Determine the cholesterol concentration of the

supernatant within 1 hour after centrifugation.

Pipette into test tubes:

Reagent blank Standard Sample

Distilled water 50 µL

Standard 50 µL

Supernatant 50 µL

Reagent (2) 1000 µL 1000 µL 1000 µL

(Cholesterol reagent)

Mix well, incubate for 10 minutes at + 20 to + 25°C

or for 5 min at 37°C and measure the absorbance of the

sample (Asample) against the reagent blank.

Calculation

Using a standard

Concentration of cholesterol in the supernatant:

 Asample __________ × concentration of std.

 Astandard

Calculation of the LDL-cholesterol

LDL-cholesterol = Total cholesterol—cholesterol in the

supernatant.

Using a Factor

Cholesterol concentration of the supernatant

= Asample × F

Factor (F) is given in table below:

mmol/L mg/dL

Hg 546 49.63 1920

500 nm 32.70 1265

Calculation the LDL-Cholesterol

LDL–cholesterol = total cholesterol— cholesterol in the

supernatant

Clinical Interpretation

mg/dL mmol/L

No treatment required < 150 3.9

Suspect range 150–190 3.9–4.9

Treatment required > 190 > 4.9

Note

Low-density lipoproteins and the very rare atherogenic Lp(a)

are precipitated qualitatively. There is a slight coprecipitation

of the VLDL but as the cholesterol content of these is low, the

LDL cholesterol values are not increased significantly and

the estimation of cardiovascular risk is not affected.

Test Significance

This test is specifically done to determine the risk of coronary

heart disease. The low-density lipoproteins are closely

correlated with an increased incidence of atherosclerosis

and coronary heart disease. One on the other hand, a

decreased incidence of coronary heart disease is seen in

persons with high levels of HDL.