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High-Density Lipoproteins (HDL)

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Overview:
HDL, often referred to as "good cholesterol", is a compound consisting of lipids (fats) and proteins. It plays a crucial role in removing excess cholesterol from the body and transporting it to the liver for processing and excretion. This function reduces the risk of atherosclerosis and cardiovascular diseases.

HDL cholesterol is the remaining cholesterol after apolipoprotein-B-containing lipoproteins (low-density lipoproteins [LDL] and very-low-density lipoproteins [VLDL]) have been deposited in the blood serum. HDL is composed of hydrophobic lipids (primarily cholesterol) and transports lipids, including cholesterol, from peripheral tissues, including blood vessels, to the liver, where it can be eliminated as fatty acids.

Since cholesterol is insoluble in water, it is transported in the bloodstream by lipoproteins, which are complexes of cholesterol and apolipoproteins. Lipoproteins are categorized as:

  • Very-Low-Density Lipoproteins (VLDL)
  • Low-Density Lipoproteins (LDL)
  • High-Density Lipoproteins (HDL)

HDL primarily contains proteins and a smaller amount of cholesterol. Its main function is to transport excess cholesterol to the liver for excretion. High levels of HDL reduce the risk of plaque buildup in the arteries, while low levels increase the risk of atherosclerosis and related complications.

HDL Cholesterol Levels and Risk of Atherosclerosis:

  • HDL <1.0 mmol/L in men and <1.3 mmol/L in women: High risk of atherosclerosis and cardiovascular diseases.
  • HDL 1.0–1.3 mmol/L in men and 1.3–1.5 mmol/L in women: Moderate risk.
  • HDL >1.55 mmol/L: Low risk, with protective effects against atherosclerosis.

HDL Levels and Cardiovascular Risk Assessment:
The atherogenic index can be calculated using the following formula:
AI = (Total Cholesterol - HDL) / HDL

  • A lower AI indicates lower cardiovascular risk.
  • For healthy individuals:
    • Men aged 20–30: AI ≈ 2.5.
    • Women aged 20–30: AI ≈ 2.2.
    • For individuals aged 40–60 without symptoms of atherosclerosis: AI ≈ 3–3.5.
    • For patients with ischemic heart disease (IHD): AI >4 (commonly 5–6).
  • Sample: Venous blood.
  • Avoid eating for 8–14 hours prior to the test.
  • Avoid physical and emotional stress before the test.
  • Do not smoke for 30 minutes before the test.
  • Diagnosis of primary lipid metabolism disorders.
  • Diagnosis of secondary lipid metabolism disorders.
  • Monitoring treatment of atherogenic lipid disorders.
  • Atherosclerosis and related diseases (e.g., coronary artery disease, myocardial infarction).
  • Liver diseases.
  • Routine and preventive screenings for individuals aged 20+ years every 5 years.
  • Early screening for children aged 2–10 years with a family history of early heart disease or elevated cholesterol.

Risk Factors for Cardiovascular Diseases:

  • Smoking.
  • Age >45 years for men, >55 years for women.
  • High blood pressure (>140/90 mmHg).
  • Family history of high cholesterol or heart disease.
  • Diabetes or obesity.
  • Alcohol consumption.
  • Diet high in animal fats.
  • Low physical activity.

Increased HDL Levels:

  • Causes:
    • Hereditary conditions (e.g., familial hypercholesterolemia).
    • Liver disorders (e.g., biliary cirrhosis, chronic hepatitis).
    • Obesity.
    • Obstructive jaundice.
    • Nephrotic syndrome, chronic kidney disease.
    • Diabetes.
    • Hypothyroidism.
    • Diets rich in cholesterol.
    • Medications (e.g., beta-blockers, statins, fibrates, estrogens).

Decreased HDL Levels:

  • Causes:
    • Atherosclerosis.
    • Hypo-alpha-lipoproteinemia.
    • Acute bacterial or viral infections.
    • Chronic liver diseases.
    • Smoking.
    • Obesity.
    • High-carbohydrate diets.
    • Stress.
    • Medications (e.g., beta-blockers, corticosteroids, anabolic steroids).