Apolipoprotein B, Plasma
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Apolipoprotein B (Apo B) is a major protein component of low-density lipoprotein (LDL) comprising >90% of the LDL proteins and constituting 20% to 25% of the total weight of LDL. Apo B exists in 2 forms. Apo B-100, the most abundant form of Apo B, is found in lipoproteins synthesized by the liver including LDL, very low-density lipoprotein, and IDL. Apo B-48 consists of the N-terminal 2152 amino acids (48%) of Apo B-100, is produced by the gut, and is found primarily in chylomicrons.
Definitive studies of cardiac risk factors in individuals with significant family histories of coronary artery disease or other increased risk factors
Follow-up studies in individuals with abnormal LDL cholesterol values
Confirmation of suspected abetalipoproteinemia or hypobetalipoproteinemia
It is well established that increased plasma concentration of Apo B-containing lipoproteins is associated with an increased risk of developing atherosclerotic disease. Case control studies have found plasma Apo B concentrations to be more discriminating than other plasma lipids and lipoproteins in identifying patients with coronary heart disease (CHD). The utility of Apo B in determining CHD risk has been confirmed by prospective studies, although the extent to which Apo B concentrations were better than serum lipids in predicting risk was variable. Apo B measurement offers greater precision than low-density lipoprotein (LDL) cholesterol determination which is most often derived by calculation.
Abetalipoproteinemia and severe hypobetalipoproteinemia can cause malabsorption of food lipids and polyneuropathy. In patients with hyperapobetalipoproteinemia (HALB), a disorder associated with increased risk of developing CHD and with an estimated prevalence of 30% in patients with premature CHD, Apo B is increased disproportionately in relation to LDL cholesterol. Apo B quantitation is required to identify these patients and is necessary in distinguishing HALB from another common lipoprotein abnormality, familial combined hyperlipidemia.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Fasting for <12 hours or intake of alcohol during the 24 hours prior to specimen collection may invalidate test results.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
> or =18 years: 48-124 mg/dL
Reference values have not been established for patients that are less than 18 years of age.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Bhatnagar D, Durrington PN: Measurement and clinical significance of apolipoprotein A-1 and B. In Handbook of Lipoprotein Testing. Edited by N Rifai, GR Warnick, MH Dominiczalc. Washington, DC, AACC Press, 1997, pp 177-198
2. Stein EA, Myers GL: Lipids, lipoproteins, and apolipoproteins. In Tietz Textbook of Clinical Chemistry, second edition. Edited by CA Burns, ER Ashwood, Philadelphia, PA, WB Saunders Company, 1994, pp 1002-1093
3. Kwiterovich PO Jr, Coresh J, Smith HA, et al: Comparison of the plasma levels of apolipoproteins B and A-1, and other risk factors in men and women with premature coronary artery disease. Am J Cardiol 1992;69:1015-1021
4. Stampfer MJ, Sacks FM, Salvini S, et al: A prospective study of cholesterol, apolipoproteins, and the risk of myocardial infarction. N Engl J Med 1991;325:373-381
5. Genest J, Marlin-Munley SS, McNamara JR, et al: Familial lipoprotein disorders in patients with premature coronary artery disease. Circulation 1992;85:2025-2033
6. Sniderman A, Shapiro S, Marpole D, et al: Association of coronary atherosclerosis with hyperapobetalipoproteinemia [increased protein but normal cholesterol levels in human plasma low density (beta) lipoproteins]. Proc Natl Acad Sci USA. 1980;77:604-608