PT - JOURNAL ARTICLE AU - Adel AA Ismail TI - When laboratory tests can mislead even when they appear plausible AID - 10.7861/clinmedicine.17-4-329 DP - 2017 Aug 01 TA - Clinical Medicine PG - 329--332 VI - 17 IP - 4 4099 - http://www.rcpjournals.org/content/17/4/329.short 4100 - http://www.rcpjournals.org/content/17/4/329.full SO - Clin Med2017 Aug 01; 17 AB - A laboratory test has three phases, pre-analytical, analytical and post-analytical. The purpose of this review is to highlight an issue concerning the analytical phase of one of the most widely deployed groups of in vitro diagnostic tests using a common technology – namely immunoassay.Immunoassay entails an inherently high error rate and, therefore, has the potential for inaccurate and misleading results susceptible to misinterpretation and/or diagnostic misapplication by clinicians. An approach based on Bayesian inference (without mathematics or equations) – illustrated by examples – is presented; this may help clinicians in discerning potentially erroneous results even when they appear plausible and not unreasonable.Essentially, false positive results are most likely to occur when the disease prevalence/incidence is low. False negative results become more prominent when the prevalence/incidence of disease increases. When concern is raised, available follow-up laboratory tests should be initiated to establish with confidence the diagnostic reliability or unreliability of such results.