Normal ranges: normal for whom?
Volume 108, Issue 3, Page 392
Mark Sigman, M.D.
While the practice of medicine has moved from art to science, laboratory testing has increased in volume. As part of our normal clinical care we often order laboratory tests and use the results, ideally in combination with the history and physical exam findings, to draw conclusions about the health or condition of our patients. Interpretation of laboratory results generally consists of comparing a patient’s lab values to the “normal range”—usually provided by the testing laboratory. Values within the normal range are interpreted as good or normal while those outside the range may indicate disease or the presence of a condition. Many of us don’t give much thought to how the reference ranges were determined. Understanding this usually neglected topic is critical to being able to interpret individual lab values. Normal values may not in fact be normal or indicative of “normal health.” Both the techniques, usually statistical, of determining normal ranges and the makeup of the population of people tested to determine those ranges have a major impact on what being within the normal range means.