LDL Cholesterol

Low-density lipoprotein (LDL cholesterol, LDL-C) is one type of lipoprotein that carries cholesterol in the blood. LDL-C consists mostly of cholesterol and similar substances with a small amount of protein. Most often, this test involves using a formula to calculate the amount of LDL-C in blood based on results of a lipid profile. Occasionally, LDL-C is measured directly.

Also Known As:  LDL, LDL-C , Low-Density Lipoprotein Cholesterol

Test Panel: Cholesterol, HDL Cholesterol, LDL Cholesterol, Triglycerides, VLDL Cholesterol, Non-High Density Lipoprotein Cholesterol

Why Get Tested :

• Advised to evaluate the coronary artery disease risk.
• This can be advised as the part of a lipid profile.

When to get tested :

• Screening: as part of a regular health exam with a lipid profile.
• when no risk factors for heart disease are present.
• once every four to six years in adults.
• children should have a lipid profile screening at least once between the ages of 9 and 11 and then again between the ages of 17 and 21.

Sample Required:

• This test is done on the serum.
• Fasting sample is preferred. Advised the patient to fast for 12 to 14 hours.
• This test can be done on plasma as well.
• Can store serum or plasma at 4 °C for 4 days (can keep for 5 to 7 days).

Normal Value:

• Adult  =  <130 mg/dL
• Children  =  <110 mg/dL

Calculation of LDL

The LDL can be calculated by the following formula:

1. LDL = Total cholesterol – ([triglycerides ÷ 5] – HDL)
2. LDL = Total cholesterol – VLDL- HDL)
3. LDL = Total cholesterol — (HDL cholesterol + 1/5 x Triglycerides)

NOTE: These formulas only help if the fasting triglycerides value is < 400 mg/ dl.

Increased LDL values are seen in:

1. Familial hyperlipidemia type 2.
2. Familial hypercholesterolemia.
3. Glycogen storage diseases.
4. Secondary causes are :
   1. Hypothyroidism.
   2. Nephrotic syndrome.
   3. Multiple myelomas.
   4. Dysglobulinemia.
   5. Liver disease with obstruction.
   6. Diabetes mellitus.
   7. Chronic renal failure.
   8. Diet high in cholesterol and saturated fats.
   9. Alcohol intake.
   10. Hepatoma.

Decreased values seen in:

1. Hypolipoproteinemia.
2. Hyperthyroidism.
3. Hyperlipoproteinemia type 1.
4. Chronic anemias.
5. Hepatocellular diseases.
6. Chronic pulmonary disease.
7. Reye’s syndrome.
8. Acute stress like a burn.
9. Inflammatory joint disease.

Table showing the summary of characteristics of the lipoproteins

Characteristics	Chylomicron	HDL	LDL	VLDL
PLasma appearance	Creamy layer, slightly turbid	Clear	Clear, or yellow-orange tint	Turbid to opaque
Size (diameter nm)	>70.0	4 to 10	19.6 to 22.7	25 to 70
Electrophoretic mobility	Origin	α – region	β – region	Pre – β region
Molecular weight	0.4 to 30 x 109	3.6 x 109	2.75 x 109	5 to 10 x 109
Synthesized in (Tissue of origin)	Intestine	Intestine and liver	Intravascular	Liver and intestine
Composition by weight in %
Cholesterol esterified	5	38	49	11 to 14
Cholesterol unesterified	2	10	13	5 to 8
Triglycerides	84	9	11	44 to 60
Phospholipids	7	22	27	20 to 23
Proteins	2	21	23	4 to 11
Triglycerides	Markedly raised	Normal	Normal/ Raised	Moderately to Markedly raised
Clinical significance of	Pancreatitis and acute abdomen	Decreased risk of CAD	Increased risk of CAD	Increased risk of CAD
Functions	Transport dietary lipids to tissue	Carry cholesterol from tissue to liver	Carries cholesterol to tissue	Transport endogenous TG from liver to adipose tissue

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Possible References Used

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