Objective To evaluate the cost-effectiveness of planned observation on cranial CT use in children with minor head trauma.

Design Planned secondary analysis of a multicentre prospective observation study.

Setting Australia and New Zealand.

Patients An analytic cohort of 18 471 children aged <18 years with Glasgow Coma Scale scores 14–15 presenting <24 hours after blunt head trauma stratified by the Pediatric Emergency Care Applied Research Network (PECARN) traumatic brain injury (TBI) risk categories.

Intervention A plan for observation and immediate CT scan were documented after the initial assessment. The planned observation group included those with planned observation and no immediate plan for CT.

Main outcome measures Taking an Australian public-funded healthcare perspective, we estimated the cost-effectiveness of planned observation on the adjusted mean costs per child and CT use reduction by net benefit regression analysis using ordinary least squares with robust SEs and bootstrapping. All costs presented in 2018 euros.

Results Planned observation in 4945 (27%) children was cost-saving of €85 (95% CI −120 to −51) with 10.4% lower CT use (95% CI 9.6 to 11.2). This strategy was cost-saving for the PECARN high-risk (−€757 (95% CI −961 to −554)) and intermediate-risk (−€52 (95% CI −99 to −4.3)) categories, with 43% (95% CI 39 to 47) and 11% (95% CI 9.6 to 12.4) lower CT use, respectively. The very low-risk category incurred more cost of €86 (95% CI 67 to 104) with planned observation and 0.05% lower CT use (95% CI −0.61 to 0.71).

Conclusion Planned ED observation in selected children with minor head trauma is cost-effective for reducing CT use for the PECARN intermediate-risk and high-risk categories.

Trial registration number ACTRN12614000463673.