In medicine, a set of values that a doctor uses to interpret a patient?s test results. The reference interval for a given test is based on test results for 95% of the healthy population. Sometimes patients whose test results are outside of the reference interval may be healthy, and some patients whose test results are within the reference interval may have a health problem. The reference interval for a test may be different for different groups of people (for example, men and women). Also called normal range, reference range, and reference values.