Clinical Chemistry and Pathologic of Biochemistry (CCPB) Practice Test

Screening immunoassays in toxicology are limited by cross-reactivity, where antibodies designed to detect a specific drug or drug class can also bind structurally related compounds. This binding can trigger a positive signal even when the target substance is absent, leading to false positives. Because of this, immunoassay results are considered preliminary and require confirmation with a more specific method, such as GC-MS or LC-MS/MS, to determine the exact compound present. Immunoassays are fast, inexpensive, and good for high-throughput screening, but they sacrifice specificity compared with chromatographic methods.