Published: 23 Apr 2024

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. In this way, ranges quoted by labs will represent the values found in 95% of individuals in the chosen 'reference' group. 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.The first step in determining a reference range is to define the population to which the range will apply. In other words, even in a 'normal' population, a test result will lie outside the reference range in 5% of cases (1 in 20). 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.

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.The first step in determining a reference range is to define the population to which the range will apply. In this way, ranges quoted by labs will represent the values found in 95% of individuals in the chosen 'reference' group. 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). 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. In other words, even in a 'normal' population, a test result will lie outside the reference range in 5% of cases (1 in 20).