Referansegrenser

Referansegrenser, eller referanseintervall, are the values that define what is considered normal for a laboratory test within a defined reference population. They are used to interpret individual test results by comparing a patient’s value against what is typical for healthy people.

Typically, referansegrenser cover the central portion of a distribution of results from healthy individuals, most commonly the middle 95%. This is often described as the 2.5th to 97.5th percentile. In practice, the exact boundaries may be influenced by the statistical method used (parametric versus non-parametric), the population sampled, and the analytical method. Many laboratories provide age- and sex-specific reference intervals, and in some cases for other subgroups (e.g., pregnancy or pediatric age groups).

Construction of referansegrenser requires careful standardization. Important factors include the selection of a healthy reference population, the calibration and harmonization of measurement methods, and appropriate statistical handling of outliers. Some analytes show variation with age, sex, ethnicity, altitude, or physiological state, leading to partitioned reference intervals. Pre-analytical factors (sample type, fasting status, time of day) and analytical factors (instrument, reagents) can also shift reference values.

Limitations exist: an abnormal result outside the reference interval does not by itself diagnose disease; conversely, a normal result does not guarantee health. Clinicians interpret results in the context of symptoms, history, and other tests. Reference ranges are provided by laboratories and may be updated as methodologies evolve or populations change.