Reference interval

A reference interval is a range of laboratory test values derived from measurements in a defined group of reference individuals. It is bounded by a lower and an upper reference limit and is used to help interpret an individual person’s test result. Reference individuals are selected according to specified criteria appropriate to the test and population being studied .¹

For many laboratory tests, reference intervals are defined to include the central 95% of values in the reference population. When this approach is used, about 5% of reference individuals will have results outside the interval simply because of how the limits are defined. A value outside a reference interval therefore does not by itself establish that a person has a disease, and a value within the interval does not necessarily exclude disease .^1,2

Reference intervals can differ between groups because some laboratory measurements vary with factors such as age or sex. They can also depend on specimen collection, analytical methods, and other laboratory conditions. For this reason, laboratories must establish or verify that a reference interval is appropriate for the population and measurement procedure in which it will be used .¹

A reference interval is distinct from a clinical decision limit. Reference intervals describe the distribution of values in a selected reference population, whereas clinical decision limits are thresholds associated with a particular diagnosis, health risk, or clinical action. Although both can appear alongside laboratory results, they are established for different purposes .²