Some clinical laboratory tests need only Yes and No or Positive and Negative to interpret but there are a vast variety of pathological tests that are interpreted based on their reference ranges (normal values). These ranges are defines as the set of values in which 95% of the normal healthy populations falls. The evolution of the reference range concept dates back to 1969 and is determined by collecting data from vast numbers of laboratory tests. In general, reference ranges are specific to the laboratory that produces the test results. The method for establishing reference range is by testing a large number of healthy people and observing what appears to be “normal” for them. Defining the reference population is very critical and demographically it should match the population whose laboratory results will be compared to this reference range.
The first step in determining a given reference range is to define the population to which the reference range will apply, for example, healthy males between 30 and 40 years old. A large number of individuals from this category would be tested for a specific laboratory test. The results would be averaged and a range (plus or minus 2 standard deviations of the average) of normal values would be established.
There are people who use the term ‘Normal Range’ instead of ‘Reference Range’. But the term Reference Range is preferred because the reference population can be clearly defined and the reference range means the results are being considered in the most relevant context. When you examine test results from different populations, you quickly discover that what is “normal” for one group is not necessarily normal for another group. For example, pregnancy changes many aspects of the body’s chemistry, so pregnant women have their own set of reference ranges.
In Pakistan, all of the laboratory tests’ references ranges we use, are based on ranges developed by international organizations many years back by testing their own population but as the references range may vary with age, sex, race, diet, use of prescribed drugs and stress, each laboratory must establish its own reference ranges using data from its own equipment and methods. At times, the existing references ranges could be misleading for the physicians as they are primarily based on a foreign population. There are many examples to quote, e.g. haemoglobin level, vitamin D level, etc. The rationale for writing this brief note is to sensitize the associations or organizations representing Pathologists and Laboratory Scientists. These are among the vital stakeholders of the system and should come forward to plan and implement studies resulting in establishment of our own references ranges.