Determination and validation of reference intervals.

A brief overview of the concept of the reference interval and its application in medical practice is presented. The populations from whom it is possible to derive reference intervals are discussed. Procedures used to develop reference intervals from both a selected healthy population and from hospitalized patients are discussed, and the influence of statistical method on presented reference intervals is reviewed. However, the weakness of using a reference interval derived from a population of individuals to facilitate interpretation of test results is illustrated in relationship to the variability of test results within an individual. In spite of the efforts that are made within the clinical laboratory through development of reference intervals to provide maximum guidance to clinicians to facilitate their proper interpretation of test values in patients, it is apparent that much of the carefully derived scientific information is ignored in actual practice.