Reference Intervals: Strengths, Weaknesses, and Challenges

A reference interval (RI)10 is a standard component of reporting a laboratory result and is important to transform a numerical value into clinically meaningful information. An RI is intended to inform the clinical care provider that laboratory values within the interval indicate a nondiseased condition. The most common approach is to base an RI on the central 95% of laboratory test values observed for a reference population that is free of diseases that influence that laboratory test result. Because many diseases are asymptomatic, it becomes difficult to qualify people for a nondiseased condition, thus biasing the selection of reference individuals. Furthermore, information on the full complement of disease conditions that influence a laboratory test may be unknown. Thus, RIs may be influenced by inappropriately selected reference populations. Another limitation in determining an RI is obtaining an adequate sample of a reference population to make an estimate of the central 95% of results with suitable uncertainty to be meaningful for interpreting a test result. The sample size requirement becomes even larger when partitioning by sex, age, ethnicity, menstrual cycle, and other parameters is necessary for meaningful RIs. CLSI Guideline EP28-A3c describes consensus approaches and some limitations for establishing and verifying RIs. However, some of the approaches in this guideline are statistically underpowered such that uncertainties in the RIs may not be appreciated. A particularly challenging situation is the requirement for laboratories to establish an RI for a laboratory developed measurement procedure (MP) or to verify the RIs proposed by the manufacturer of an in vitro diagnostic (IVD) MP. Identifying a suitable reference population for either requirement can be very challenging. Evolution in laboratory practice is needed to enable appropriate RIs to be adopted by laboratories. We asked experts with different perspectives to address issues we all face in establishing or …