Measurement Signal Versus Value in Immunoassays for Human Plasmaproteins

Abstract

Signal size proportionality to a measurement value will be obtained in immunoassays only if the following four - theoretical - postulates are fulfilled: The immunochemical reaction behaviour (number and affinity of the epitopes) of the protein analyzed is identical and uniform for both the reference preparations (Standard/Calibrator/Control) and for the analyte in the specimens (uniform physicochemical properties of the proteins). The immunochemical reaction behaviour of the antibody/ies containing reagent used in the immunoassay is identical and uniform from batch to batch with respect to the reactive antibody population. The immunochemical method is so well standardized with the consequence that the size of the measurement signal - caused only by the antigen antibody reaction product - will not be falsified (by matrix-and other interfering influences, or by the method principle). The values for the results of plasma protein determination are declared by arbitrary units, e.g. international units (IU). As a rule conversion factors to g/L (SI units) are not constant and depend on very many effects. It is very difficult to fulfill all the four theoretical postulates. Therefore the practical consideration of the medical requirements should be taken into account and should be the guideline for approachable solutions.