title: Effect of variability of plasma interferences on the accuracy of drug immunoassays.
abstract: Most immunoassays applied to drugs in human plasma do not use an extraction of analyte. To compensate for interferences due to plasma proteins or salts, standards are prepared in drug-free plasma. Because the concentration of plasma components varies from one subject to another, it is likely that the drug-free plasma is not representative of the potential interference in each plasma. Using two immunoassays, for a steroid (nomegestrol acetate) and a heptapeptide (BN 52080), the authors have shown that tracer binding to the antibody may vary significantly between plasma from different subjects. Intersubject variability of tracer-antibody binding was 21.6% (coefficient of variation for 25 subjects) for nomegestrol acetate. When the same plasma were spiked with the steroid at a concentration corresponding to the central part of the standard curve, the recovery was between 39 and 215%. Intersubject variability in tracer binding was lower (7.7%) for the peptide immunoassay, but still affected accuracy. The authors show that this problem is common to direct immunoassays for other drugs and must be solved in assay development.
authors.affiliation: Commissariat à l'Energie Atomique, Service de Pharmacologie et d'Immunologie, Gif-sur-Yvette, France.
authors.forename: E
authors.initials: E
authors.lastname: Ezan
authors.forename: A
authors.initials: A
authors.lastname: Emmanuel
authors.forename: D
authors.initials: D
authors.lastname: Valente
authors.forename: J M
authors.initials: JM
authors.lastname: Grognet
mesh_terms: D016903:Drug Monitoring; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D010949:Plasma / Q000276:immunology*