Although several immunoassays do not currently yield high numbers of false positives, others do and these can be simply explained by some degree of structural similarity with the immunoassay antigen. Additional DOA/Tox immunoassays for some therapeutic drug classes (e.g., benzodiazepines, opiates) possess high levels of false negatives resulting from newer drugs which may have comparatively lower structural similarity with the immunoassay antigenic target. ED physicians should therefore be aware of substantial variability in different marketed assays with respect to cross-reactivity Inhibitors,research,lifescience,medical of drugs, metabolites, and natural products.

There is a current need for improved immunoassays or novel more specific technologies and closer Inhibitors,research,lifescience,medical tracking of prescribing trends for drugs likely to cross-react with DOA/Tox immunoassays. Competing interests The authors

declare that they have no competing interests. Authors’ contributions MDK conceived of the study and structured the data. MDK and SE drafted the manuscript. AFP NSC 23766 price participated in the planning of the study, interpretation of data, and the historical data analysis. MGS and Inhibitors,research,lifescience,medical SG performed and analyzed the laboratory studies involving immunoassays and GC/MS. SE and MI performed the computational analyses. All authors participated in editing and Inhibitors,research,lifescience,medical revising the manuscript and approved the final version.

Pre-publication history The pre-publication history for this paper can be accessed here: http://www.biomedcentral.com/1471-227X/9/5/prepub Supplementary Material Additional file 1: Similarity data and tricylic antidepressant/phencyclidine assay data. Spreadsheet with multiple Inhibitors,research,lifescience,medical tables contains data on similarity analyses, marketed assays, most prescribed medications, and cross-reactivity studies for phencyclidine and tricyclic antidepressant assays. Click here for file(454K, xls) Additional file 2: Historical trends in prescription drug usage in the United States that can impact drug of abuse testing. Data on trends in prescription drugs usage is presented by classes of drugs. Click here for file(758K, pdf) Acknowledgements The authors thank Darla Lower and Jackie Rymer for technical Thiamine-diphosphate kinase assistance, and Melissa Ratajeski and Ahlam Saleh (reference librarians, University of Pittsburgh Health Sciences Library System) for help in locating published data on drug prescriptions in the United States. SE gratefully acknowledges Accelrys, Inc. (San Diego, CA) for making Discovery Studio available. This research was supported by National Institutes of Health grant K08-GM074238 to MDK.