The interpretation of any clinical laboratory test is done by comparing the patient's results to the test's reference intervals. For example, the reference interval for white blood cells (WBC) in human adults is 4,500-11,000 cells/microlitre. Estimation of this reference interval is done by testing
1
a large number of healthy adults and estimating the range between 2.5 to 97.5 percentiles of the reference population.
2
a large number of healthy adults and estimating the range between 5 to 95 percentiles of the reference population.
3
a large number of random adults and estimating the range between 5 to 95 percentiles of the reference population.
4
a large number of random adults and estimating the range between -1.64 and +1.64 standard deviations either side of the mean of the reference population.