Apolipoprotein assays: standardization and quality control.

A correct approach to standardization, accuracy-based methods, and well-defined quality assurance programs is indispensable for the definition of international reference intervals of apo A-I and apo B. Variability in the immunochemical determination of apo A-I and apo B can be due to both preanalytical and analytical variations, and standardized laboratories should evaluate and minimize each source of error in determining the reference intervals. A key requirement to reduce the variation between measurement techniques is the use of a common protocol for the calibration of the different methods. The basis of a calibration system is the primary standard with the absolute mass accurately determined. The primary standard is indispensable in assigning an accurate target value to reference materials with a reference method in which the primary standard immunochemically reacts the same as the protein in plasma. The reference material, which must behave immunochemically the same as the patient's sample in all methods, is then used to assign a target value to the calibrator in each method and system. Following this procedure, all assay results can be traced back to the primary standard via the serum reference material. The development and distribution of reference and quality control materials, which do not exhibit matrix effects between methods, is fundamental for the standardization process.