When "Normal" Doesn't Matter
For some tests, such as cholesterol, rather than worry about the reference range, the vast majority of people need only be concerned if their test result falls above or below a cut-off value that is sometimes referred to as a "decision point". If, for example, as studies have shown, a cholesterol level of 200 milligrams per deciliter is the cut-off where heart disease risk should trigger medical intervention, then it doesn't really matter if this result falls into a statistically "normal" range.
There are additional tests for which the "normal" range is irrelevant. In testing for the amount of a drug in the blood of an unconscious person, for example, the doctor will interpret the result in terms of the likely effects of the drug at the detected level, not in terms of a reference range.
In addition, clinically significant, dramatic changes in a person's test values, even if those values remain within the reference range for that test, should be brought to the doctor's attention.