Reference interval

Reference interval is a range of values that is deemed normal for a physiological measurement in healthy persons (for example, the amount of glucose in the blood). It is a basis for comparison for a patient's results. If a patient's results fall outside this interval, it may indicate disease.

Definition

The reference interval is defined by the Clinical and Laboratory Standards Institute (CLSI) as the interval between which 95% of values of a reference population fall into. This is based on the assumption that the distribution of values in the population is normal, or bell-shaped. However, many laboratory values do not have a normal distribution, and in these cases, a non-parametric method is used to determine the reference interval.

Determination

The reference interval is determined by collecting data from a large number of healthy individuals and calculating the 2.5th and 97.5th percentiles. This means that 5% of healthy individuals will have values outside the reference interval. The reference population should be representative of the patients to whom the reference interval will be applied. Factors such as age, sex, and race may affect laboratory values and should be taken into account when selecting the reference population.

Use in medical practice

In medical practice, the reference interval is used to interpret a patient's laboratory results. If a result falls outside the reference interval, it may indicate disease. However, a result within the reference interval does not necessarily mean that the patient is healthy. The reference interval is just one tool that clinicians use in the diagnosis and management of disease.

Limitations

There are several limitations to the use of reference intervals. First, they are based on population data and may not be applicable to all individuals. Second, they do not take into account the natural variation in laboratory values. Third, they do not provide information about the severity or cause of disease.

See also

• Clinical pathology
• Medical laboratory
• Laboratory test

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