[Abnormal laboratory results : Plausibility, reliability, and implications]

In outpatient care or the emergency room laboratory tests oftentimes provide the first clues to the medical condition that made the patient seek medical help. Quite commonly, rapid medical decisions are required in these situations. Therefore, laboratory results must be evaluated immediately and interpreted within the broader context of the patient's presentation. During this process test results must be checked for plausibility, their positive and/or negative predictive values for the individual patient must be considered, and finally, the potential clinical implications need to be assessed. The latter in particular is of the utmost importance. This article discusses several laboratory tests commonly ordered for emergency patients and provides some guidance on their relevance in the decision to refer an outpatient to an emergency room or for inpatient care, or whether a patient can be safely diagnosed in the outpatient setting.