Published: 30 Jul 2023

These intervals are thought of as 'normal ranges or limits.
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Though the term 'reference interval' is usually the term preferred by laboratory and other health professionals, the more commonly-known term is 'reference range,' so that is the term used throughout this article.
Reference ranges provide the values to which your health care provider compares your test results to and determines your current health status. However, the true meaning of a test result-whether it indicates that you are sick or well or at risk for a health condition-can only be known when all the other information your provider has gathered about your health, including the results of a physical exam, your health and family history, recent changes in your health, any medications you are taking, and other non-laboratory testing.A reference range is a set of values that includes upper and lower limits of a lab test based on a group of otherwise healthy people. The values in between those limits may depend on such factors as age, sex, and specimen type (blood, urine, spinal fluid, etc.) and can also be influenced by circumstantial situations such as fasting and exercise.

In other words, even in a 'normal' population, a test result will lie outside the reference range in 5% of cases (1 in 20). In this way, ranges quoted by labs will represent the values found in 95% of individuals in the chosen 'reference' group. The first step in determining a reference range is to define the population to which the range will apply. The reference range is then derived mathematically by taking the average value for the group and allowing for natural variation around that value (plus or minus 2 standard deviations from the average). A large number of individuals from a group who are thought to represent a 'normal' population, will be tested for a particular laboratory test. Indeed for tests such as cholesterol the idea of a normal range has been replaced to a large extent by use of target values, achieved either by lifestyle changes or active treatment.
Whether or not your test result is within the laboratory reference range, the result must be considered within the context of your personal circumstances, and with the benefit of your doctor's knowledge of your past medical history, current medication and the results of any other investigations.This is why the term 'reference range' is preferred over 'normal range'.
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.