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Clinical Chemistry 48: 405-406, 2002;
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(Clinical Chemistry. 2002;48:405-406.)
© 2002 American Association for Clinical Chemistry, Inc.

Editorial

Unexpected Suppression of Immunoassay Results by Cross-Reactivity: Now a Demonstrated Cause for Concern

Roland Valdes, Jr.1,2a and Saeed A. Jortani1

Departments of
1 Pathology and Laboratory Medicine and
2 Biochemistry and Molecular Biology, University of Louisville School of Medicin, Louisville, KY 40292

aAddress correspondence to this author at: Department of Pathology and Laboratory Medicine, University of Louisville School of Medicine, Louisville, KY 40292. Fax 502-852-7674; e-mail rvaldes@louisville.edu.

More than other analytical procedures, immunoassays have afforded a wealth of knowledge about biochemical physiology over the last 40 years. These assays have posed major analytical challenges, which most likely stem from the delicate balance between chemical equilibrium and our ever-increasing quest for speed of analysis, simplicity of procedure, and improved reliability. In attempts to enhance these criteria, we often face limitations imposed by the fundamental principles of thermodynamics: balancing chemical equilibrium, the underlying kinetics, and that ever-present variable, time.

Cross-reactivity in competitive immunoassays can be measured by various methods, including 50% displacement, equal displacement, or the gradient approach (1). Typically, a cross-reactant is conceptually regarded as an interferent causing positive bias in the assay results. When an immunoassay is "rushed" (i.e., the signal is measured well before reaching equilibrium), the effect of the cross-reactant is enhanced, in essence increasing the positive bias (2). That is the expected phenomenon. The unexpected is the observation that cross-reactivity can also lead to suppression in recovery (3), i.e., a negative bias. In other words, the result obtained for a constant amount of the analyte in a sample is lower when the cross-reactant is present than when it is absent. This indicates that rigorous characterization of cross-reactivity requires studies in the presence of the analyte (1).

Suppression of assay results induced by cross-reactivity was first described in Clinical Chemistry in 1996 for digoxin immunoassays (4). In retrospect, however, previous observations hinted at this problem. Kanan et al. (5) reported that . . . [Full Text of this Article]


References




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