Published: 12 Oct 2024

To determine a reference range, the first step is to define the population it will apply to.
A large number of individuals from what is considered a 'normal' population are tested. The reference range is calculated by averaging the values and accounting for natural variations (plus or minus 2 standard deviations). This represents the values found in 95% of the chosen group. This is why 'reference range' is preferred over 'normal range' since even in a 'normal' population, 5% of test results will fall outside this range.

When examining different populations, what's 'normal' for one group may not be for another. For example, with cholesterol tests, the concept of a normal range has largely been replaced by target values achieved through lifestyle changes or treatment.

Your test result, whether within the reference range or not, must be considered in the context of your personal circumstances, medical history, current medication, and other investigation results.

Blood samples are typically taken to analyze various health aspects, allowing doctors to diagnose potential blood-related and non-blood-related disorders, monitor conditions, and evaluate treatment effectiveness. Factors measured during laboratory analysis include complete blood count, hormone and electrolyte levels, types of leukocytes, and blood plasma protein levels.

By analyzing the patient's blood properties and comparing them to healthy or normal values, known as 'reference ranges,' the presence or absence of various medical conditions can be established.