Interpretating Normal Values and Reference Ranges for Laboratory Tests

Laboratory test results drive about 70% of clinical decisions and are important in making diagnosis, prognosis, ruling out conditions, testing for propensity to disease and monitoring the course of illnesses. The requirement for releasing laboratory results to patients has altered the dynamics of doctor patient interaction. Minor variations in laboratory test results that are labeled by the laboratory as low/high/abnormal may cause unwarranted worry to the patients. The number of laboratory results that are outside the "normal range" far exceeds the clinically meaningful abnormal results due to the usually accepted methodology for ascertaining "normal values"/reference ranges, variations in methods of testing at different laboratories, variations due to age, gender, ethnicity, seasonality, and random variations. The usual process for establishing "normal values/reference ranges" entails testing at least 120 healthy individuals in a given age-group, gender, ethnicity, testing method and related health issues. The central 95% of the values is usually adopted as the normal range. This practice, by definition, labels 5% of healthy individuals as having abnormal laboratory results. This review addresses various issues that affect laboratory test results and interpretation of such results. It also addresses doctor and patient concerns about assessing and reporting laboratory results. In addition to reporting normal values along with patient results, it may be useful to include clinical significance of the findings, in simple terms, such as, no immediate concern, warrants discussion with doctor at the next visit, recommend contacting your doctor for further action.