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Apolipoprotein B (Apo B)

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Apolipoprotein B is a plasma protein that forms an integral component of low-density lipoproteins (LDL). Increased Apo B levels indicate a high risk of cardiovascular disease (CVD). Apolipoproteins are essential structural components of lipoproteins, which transport lipids in the blood.

There are two types of Apo B in humans:

  1. Apo B-100:

    • Synthesized in the liver.
    • Found in all atherogenic lipoprotein fractions (LDL, very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL)).
    • Apo B-100 is crucial for LDL synthesis.

  2. Apo B-48:

    • Synthesized in the intestine.
    • Vital for chylomicrons, which transport dietary lipids from the intestine to the liver.

Apo B is critical for lipoprotein recognition and binding to specific receptors on cell membranes, enabling cellular lipid uptake. Measurement of Apo B-100 reflects LDL concentration in the blood and is considered a more precise marker for assessing CVD risk than LDL cholesterol alone.

The combined assessment of Apo A1 (HDL component) and Apo B and their ratio (Apo B/Apo A1) provides a comprehensive evaluation of lipid metabolism disorders, atherosclerosis, and coronary heart disease (CHD).

  • Apo B/Apo A1 ratio:
    • Risk for coronary artery disease: >0.9 in men, >0.8 in women.
    • Apo A1/Apo B ratio >1.1 is protective.
  • Sample: Venous blood.
  • Fasting for 12 hours (minimum 8 hours, not exceeding 14 hours) before the test.
  • Avoid physical and emotional stress.
  • Refrain from smoking for 30 minutes before the test.
  • Risk assessment for ischemic heart disease (IHD).
  • Diagnosis of hereditary lipid metabolism disorders.
  • Evaluation of cardiovascular disease risk and complications.
  • Calculation of Apo B/Apo A1 ratio as a substitute or supplement to other cardiovascular risk assessments.
  • Monitoring after detecting high cholesterol.
  • Early-onset cardiovascular disease or complications in the patient or relatives.
  • Suspected deficiency or excess of Apo B.
  • Family history of IHD or hyperlipidemia, especially in cases with high triglycerides where LDL results may be difficult to interpret.
  • High CVD risk from previous tests, poor dietary habits (animal fats), or lipid-lowering therapy (e.g., statins) to assess treatment goals.

Risk factors include:

  • Age: >45 years (men), >55 years (women).
  • High blood pressure: >140/90 mmHg.
  • Family history of high cholesterol or CVD (men <55 years, women <65 years).
  • Diabetes and obesity.
  • Alcohol consumption or diets high in animal fats.

    Clinical Significance:

    Elevated Apo B Levels:

  • Indicate increased LDL and other atherogenic lipoproteins, contributing to plaque formation and CVD.
  • May occur due to a genetic mutation in the Apo B gene, impairing LDL receptor recognition and clearance.
  • Conditions associated with high Apo B levels:
    • Familial hyperlipidemia.
    • Acute-phase reactions (elevated in acute illnesses).
    • Metabolic syndrome, obesity, and type 2 diabetes.
    • Hypothyroidism.
    • Nephrotic syndrome.

  • Apo B/Apo A1 Ratio:

  • A higher ratio suggests a greater risk of atherosclerosis and CVD.
  • Monitoring this ratio can guide preventive or therapeutic strategies.
  • Familial Hypercholesterolemia
  • Hyperapobetalipoproteinemia (Normal HDL, elevated Apo B)
  • Hyperlipoproteinemia Types II, IV, V
  • Familial Combined Hyperlipidemia
  • Familial Apo B-100 Deficiency
  • Ischemic Heart Disease, Nephrotic Syndrome
  • Atherosclerosis, Coronary Artery Disease, Myocardial Infarction
  • Diabetes Mellitus, Hypothyroidism
  • Liver Diseases, bile duct obstruction, cholestasis (hepatitis, liver cirrhosis, gallstones)
  • Cushing's Syndrome, Porphyria
  • Chronic Kidney Disease
  • Polygenic (sporadic) Hypercholesterolemia
  • Pregnancy (testing is recommended no earlier than six weeks postpartum)
  • Smoking
  • Obesity
  • Sedentary Lifestyle
  • Diet high in saturated fats and cholesterol
  • Medications: Anabolic steroids, androgens, diuretics, catecholamines, glucocorticoids, progestins, beta-blockers, cyclosporine

    Reduced Apolipoprotein B Levels:

  • Abetalipoproteinemia (rare genetic condition; Apo B synthesis is disrupted; LDL and VLDL levels decrease)
  • Familial Hypobetalipoproteinemia
  • Hyperthyroidism
  • Liver Diseases
  • Malabsorption Syndrome
  • Chronic Anemias
  • Severe Hepatocellular Dysfunction
  • Inflammatory Joint Diseases
  • Multiple Myeloma
  • Infectious Diseases and Inflammatory Processes
  • Uncontrolled Diabetes Mellitus
  • Severe Burns
  • Alcoholism
  • Prolonged Fasting
  • Intense Physical Work
  • Diet low in cholesterol and saturated fats but rich in polyunsaturated fatty acids
  • Menopause
  • Weight Loss
  • Medications: Statins, fibrates, phenobarbital, oral contraceptives, thyroxine, estrogens, cholestyramine