Background Low-value use of laboratory tests is a global challenge. Our objective was to evaluate an intervention bundle to reduce repetitive use of routine laboratory testing in hospitalised patients.

Methods We used a stepped-wedge design to implement an intervention bundle across eight medical units. Our intervention included educational tools and social comparison reports followed by peer-facilitated report discussion sessions. The study spanned October 2020–June 2021, divided into control, feasibility testing, intervention and a follow-up period. The primary outcomes were the number and costs of routine laboratory tests ordered per patient-day. We used generalised linear mixed models, and analyses were by intention to treat.

Results We included a total of 125 854 patient-days. Patient groups were similar in age, sex, Charlson Comorbidity Index and length of stay during the control, intervention and follow-up periods. From the control to the follow-up period, there was a 14% (incidence rate ratio (IRR)=0.86, 95% CI 0.79 to 0.92) overall reduction in ordering of routine tests with the intervention, along with a 14% (β coefficient=−0.14, 95% CI −0.07 to –0.21) reduction in costs of routine testing. This amounted to a total cost savings of $C1.15 per patient-day. There was also a 15% (IRR=0.85, 95% CI 0.79, 0.92) reduction in ordering of all common tests with the intervention and a 20% (IRR=1.20, 95% CI 1.10 to 1.30) increase in routine test-free patient-days. No worsening was noted in patient safety endpoints with the intervention.

Conclusions A multifaceted intervention bundle using education and facilitated multilevel social comparison was associated with a safe and effective reduction in use of routine daily laboratory testing in hospitals. Further research is needed to understand how system-level interventions may increase this effect and which intervention elements are necessary to sustain results.