emDocs - June 15, 2021 - By Andrew and Ann-Jeannette Geib
Reviewed by: Cynthia Santos; Alex Koyfman; and Brit Long
- “Introduction
- Many studies have argued against the benefit of urine drug screens (UDS) in the emergency department, and in the setting of emergent psychiatric evaluation. These studies cite high costs associated with the UDS, increased length of stay (LOS), and lack of alteration in patient management. Additionally, the interpretation of the typical UDS, an immunoassay of typical drugs of abuse, is fraught with a high potential for false positives and false negatives1.
- The immunoassay is a bioanalytical method that uses the reaction of an antigen (analyte) with an antibody, and is used in the typical point of care UDS to determine the presence or absence of a drug in the urine. Each immunoassay tests for a specific analyte, and has a set cutoff above which a concentration of said analyte will yield a positive result. Because of either limited or cross-reactivity, immunoassays are subject to a large number of false positives and false negatives2.
- A number of substances can cross-react with structurally related and unrelated compounds in the system to produce a positive result.
- False negatives occur due to a variety of reasons, including antibody interference, a high concentration cutoff for a positive result, and duration between drug dosing and the time the sample is obtained for analysis…“