Reference Intervals for Clinical Laboratories

Reference intervals (RIs) are a fundamental tool in many medical disciplines for interpreting patient laboratory test results in clinical laboratories. Ideally, they enable the differentiation of healthy and unhealthy individuals. Clinical laboratories must establish accurate RIs, which is a very important process. Traditionally, RIs have been estimated using the 'direct' approach, which involves collecting laboratory test results from apparently healthy volunteers. An alternative approach is the 'indirect' approach, in which results from specimens collected for routine, screening, diagnostic or monitoring purposes are used to determine the RIs. When a laboratory receives an RI from the literature, manufacturers or another laboratory, the process of confirming its suitability for use is usually referred to as 'verification of RIs'. This raises questions about the transferability of RIs that need to be addressed. Common RIs can be obtained from multicentre studies, providing an opportunity to harmonise RIs within a given population. Clinical decision limits (CDLs) lead to the decision that individuals with values above or below the decision limit should be treated differently. There is still some confusion surrounding the difference between RIs and CDLs. The challenging groups, such as pediatric, geriatric and gestational age groups, as well as for uncommon sample types is a gap in the RIs studies. When individuality is a key factor, personalised RIs are far more effective than population-based RIs for monitoring  individuals.