Apolipoproteins (APO) A-1 and B

Definition

An apolipoprotein is a protein component of lipoprotein, whose main function is to transport lipids. Apolipoproteins play an important role in maintaining structural integrity and solubility of lipoproteins and play an important role in lipoprotein receptor recognition and regulation of certain enzymes in lipoprotein metabolism. Apolipoprotein A (apo-A; also known as Apo A-1) is the major protein (90%) of HDL. Apolipoprotein B (apo B) is major protein component of low-density lipoprotein and is important in regulating cholesterol synthesis and metabolism.
Normal range:
- Apo A-1
  - Male: 94 " “178 mg/dL
  - Female: 101 " “199 mg/dL
- Apo B
  - Male: 55 " “140 mg/dL
  - Female: 55 " “125 mg/dL
- Apo B/A-1 ratio
  - One half risk
  - Male: 0.4
  - Female: 0.3
- Average risk:
  - Male: 1.0
  - Female: 0.9
- Twice average risk:
  - Male: 1.6
  - Female: 1.5

To evaluate the risk of CAD: Levels of apo A-1 are inversely associated with premature cardiovascular disease and peripheral vascular disease. The ratio of apo A to apo B has greater sensitivity and specificity for CAD than individual lipid or lipoproteins.
To evaluate atherosclerotic disease.
To detect Tangier disease.

Drugs that affect apo A-1:
- Increased: carbamazepine, estrogens, ethanol, lovastatin, niacin, oral contraceptives, phenobarbital, pravastatin, simvastatin
- Decreased: androgens, beta blockers, diuretics, and progestins
Other factors that affect apo A-1:
- Increased: exercise
- Decreased: smoking, pregnancy, diet high in polyunsaturated fats, and weight reduction
Drugs that affect apo B:
- Increased: androgens, beta blockers, diuretics, progestins
- Decreased: estrogen, lovastatin, simvastatin, niacin, and thyroxine
Other factors that affect apo B:
- Increased: pregnancy
- Decreased: diet high in polyunsaturated fats and low cholesterol, weight reduction
Other: apo A-1 and apo B are acute-phase reactants and thus should not measured in sick patients.