Standardization of apolipoprotein B and A-I measurements.

Apolipoprotein B, the major protein of low-density lipoprotein, and apolipoprotein A-I, the major protein of high-density lipoprotein, can serve as important predictors of atherosclerotic cardiovascular disease. However, these apolipoprotein measurements have not realized their full potential because of inadequate standardization. Purified apolipoprotein A-I of known absolute mass, in lyophilized form, can serve as primary standard for apolipoprotein A-I, and freshly isolated low-density lipoprotein of narrow density range can serve as primary standard for apolipoprotein B. These primary standards can be used to assign target values to secondary reference material and calibrators by reference laboratories using standardized, validated immunoassay procedures. Lyophilized serum can serve as secondary reference material for apolipoprotein A-I. Freshly frozen serum pools should be used as reference material for apolipoprotein B until more practicable materials that do not exhibit matrix interactions are developed. Implementation of proper standardization procedures can lead to significant improvements in apolipoprotein measurements.