Reference Ranges

According to Wikipedia, reference ranges in health-related fields are generally defined as “the prediction interval between which 95% of values of a reference group fall into, in such a way that 2.5% of the time a sample value will be less than the lower limits of this interval, and 2.5% of the time it will be larger than the upper limit of this interval, whatever the distribution of these values.”

In other words, reference ranges are important! They provide the necessary context for medical analysis and diagnosis. Without a reference range (also sometimes referred to as reference value or reference interval) medical professionals have no comparison group for which to make diagnosis and advise treatment.

In all instances where reference ranges are used, context is key. In sub-Saharan Africa many labs use European established reference ranges which represent a primarily Caucasian population. This is because reference ranges specific to populations in sub-Saharan Africa do not universally exist. This presents a problem as many factors can contribute to what is considered “normal” in different populations. Genetics, dietary patterns, pregnancy, gender, age, ethnic origin, and prior exposure to pathogens all can influence reference range values.

Establishing accurate reference ranges for a given population takes time and an enormous amount of resources. It is often recommended that laboratories establish their own reference ranges based upon the population that they serve. This is cost and resource prohibitive for many laboratories in the developing world. In absence of region specific reference ranges, it is recommended that each lab validate existing ranges using their own population. However, even this can be prohibitive in resource (both physical and human) limited settings.

This can lead to egregious errors in disease diagnosis and treatment. Clement Zeh, Collins Odihiambo and Lisa Mills write that reference range research thus far reveals that African populations differ from their European/Caucasian counterparts with lower hemoglobin, red blood cell counts, hematocrit, mean corpuscular volume, platelet counts, and neutrophil counts  and higher monocyte and eosinophil counts (see for their chapter on Laboratory Reference Intervals in Africa).

In addition to diagnosis and treatment of individuals, reference ranges are crucial components in drug and vaccine studies. Historically, clinical trials of drugs and vaccines have relied upon ranges developed in the Western world. This can have significant impact upon the research data resulting in health risks to study participants, poor data, and huge amounts of resources wasted.

Thus, while it is costly and time consuming, reference ranges specific to populations in countries in the developing world need to be established. This would help both the treatment of individuals, and the testing, study and development of important vaccines and drugs.

-Marie Levy

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