Mean Abnormal Result Rate: Proof of Concept of a New Metric for Benchmarking Selectivity in Laboratory Test Ordering

Objectives: There is a need to develop and validate new metrics to access the appropriateness of laboratory test requests.

Methods: The mean abnormal result rate (MARR) is a proposed measure of ordering selectivity, the premise being that higher mean abnormal rates represent more selective test ordering. As a validation of this metric, we compared the abnormal rate of lab tests with the number of tests ordered on the same requisition. We hypothesized that requisitions with larger numbers of requested tests represent less selective test ordering and therefore would have a lower overall abnormal rate.

Results: We examined 3,864,083 tests ordered on 451,895 requisitions and found that the MARR decreased from about 25% if one test was ordered to about 7% if nine or more tests were ordered, consistent with less selectivity when more tests were ordered. We then examined the MARR for community-based testing for 1,340 family physicians and found both a wide variation in MARR as well as an inverse relationship between the total tests ordered per year per physician and the physician-specific MARR.

Conclusions: The proposed metric represents a new utilization metric for benchmarking relative selectivity of test orders among physicians.