Background: Laboratory test ordering is one of the most important clinical acts performed by family physicians. One in three laboratory test orders has been shown to be inappropriate. Inappropriate laboratory tests result in a waste of resources and are potentially harmful. False-positive tests and coincidental findings may result in unnecessary ‘downstream’ diagnostic testing or treatments.

Objectives: To evaluate the effect of evidence-based order sets on quantity and quality of laboratory test ordering in primary care.

Methods: The intervention of this cluster randomised-controlled trial (RCT) is a form of decision support consisting of order sets derived from national evidence-based recommendations as formulated by the Flemish College of General Practitioners. These order sets will be integrated within an online computerised physician order entry (CPOE) linked to every electronic health record in Belgium (EHR). After recruitment, primary care practices will be randomised to an intervention or control arm. The primary outcome of interest is the number and proportion of appropriate tests in both groups. Additionally, we will investigate the effects of the orders sets on diagnostic error, ‘downstream’ activities and laboratory test volume. Collecting data will be done nationwide according to novel standards with healthdata.be.

Results: Preliminary results will be presented.

Conclusions: Several studies have shown promising effects of decision support on volume of laboratory tests, but limited information exists. Our study is designed to collect data allowing us to evaluate not only test volume but also test appropriateness. No studies have been conducted evaluating the effect of decision support of diagnostic error. Our study will contribute important information on this subject.