What is a reference range?

• A. The range of values that encompasses the central 95% of a healthy population, used to interpret patient results.
• B. The maximum value observed in a single patient over a year.
• C. The procedural limit of measurement.
• D. The total allowable error for a test.

Answer: (A)

A reference range is the interval of values expected for a healthy person. It typically covers the central 95% of results from a healthy population, so a test result within this range is considered normal for interpretation purposes. This helps clinicians decide whether a patient’s result is likely normal or may indicate a need for further evaluation. The range is derived from population studies and can vary by age, sex, and the specific laboratory method or instrument used. It’s not the maximum value seen in one patient, nor a measurement limit or an allowable error. For example, a liver enzyme like ALT might have a reference range of about 7–56 U/L in adults; a result above this range would be considered elevated and could prompt additional assessment. Pre-analytical factors and assay differences can influence the exact numbers, so clinicians often refer to the lab’s specific reference intervals for accurate interpretation.