The interpretation of any diagnostic laboratory test involves comparing the patient's results with the test's 'reference range'.
Determining a reference range
Reference ranges are a guide for clinical decision making and are not absolute. The 'normal' ranges are dependent on the population of interest and on the laboratory assay in use. For many parameters, there is significant variation in 'normal' ranges dependent on age, breed and physiological state (e.g. fitness/training, reproductive state, environmental factors). When calculating reference ranges, a large number of individuals from a group who are thought to represent a 'normal' population are tested for a particular assay. 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). As well as the variation in the population of horses, variation does occur between assays/machines and, wherever possible, ranges should be calculated specifically for each laboratory.
Our current reference ranges can be downloaded and printed, as required. References for individual assays are also provided in the A to Z list of tests.