biological reference interval

A biological reference interval describes the distribution of examination values in a defined reference population under specified conditions. It commonly represents the central portion of that distribution, often the central 95 percent, but the chosen approach must be stated. Some healthy reference individuals therefore fall outside the interval, and some patients with disease have results within it.

Reference intervals can depend on age, sex, physiological state, population characteristics, specimen conditions, and examination procedure. The laboratory needs evidence that an interval is appropriate for its users and method, whether established locally or adopted after suitable review and verification. A clinical decision limit serves a different purpose: it links a value to a diagnostic or management decision and should not automatically be treated as a reference interval.

For accreditation, appropriate intervals and decision limits support safe interpretation of reports. Document their sources, applicability, verification, and review after relevant method or population changes. Ensure that reporting systems apply the correct partition and units. Staff should understand that an out-of-range flag alone does not establish a diagnosis or determine whether a result is critical.