Reference values

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Accurate reference values are essential for the correct interpretation of laboratory tests and clinical decision-making. Reference values should be established by testing a large number of healthy individuals. The results are then averaged and a range (plus or minus 2 standard deviations of the mean) of ‘normal’ values are established. The reference range of a test may be affected by the age and sex of the patient, and the variation is higher in some tests than in others.  Because of this, reference values should be divided in groups according to age and gender, and ideally also according to ethnicity and geographical region.

Different laboratories use different kinds of equipment and testing methods, and therefore each laboratory must establish its own reference ranges using their own results data. Theoretical reference ranges exist but they are far from being standard and each laboratory should supply its own reference values, which are true for the local population, when reporting the results of a test.

Establishing locally derived reference ranges can be challenging as it requires selecting the right reference population and collecting and processing large numbers of samples from individuals that meet the inclusion criteria and represent relevant demographic groups. Because of this, many laboratories in resource-constrained settings use values from Western populations as reference, although previous studies have found significant differences between populations from distinct geographical regions or ethnicity.

Plos One recently published three articles about research groups in different parts of Africa (Nigeria, Mozambique and Botswana) working to establish haematology and clinical chemistry reference rangesfor their local healthy adult populations. The studies showed significant gender differences, as previously known, but more importantly, they demonstrated significant differences in normal laboratory ranges between the studied populations and other African and Western populations. Such dissimilarities could be due to differences in geographical locations, climate, dietary habits, and environmental factors or distinct ethnic characteristics.

The findings of these studies underscore the need to establish region-specific clinical reference ranges for different populations in order to improve the interpretation of laboratory test results and health care delivery.

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