BACKGROUND: Clinical decision rules (CDRs) for paediatric head injury (HI) exist 
to identify children at risk of traumatic brain injury. Those of the highest 
quality are the Canadian assessment of tomography for childhood head injury 
(CATCH), Children's head injury algorithm for the prediction of important 
clinical events (CHALICE) and Pediatric Emergency Care Applied Research Network 
(PECARN) CDRs. They target different cohorts of children with HI and have not 
been compared in the same setting. We set out to quantify the proportion of 
children with HI to which each CDR was applicable.
METHODS: Consecutive children presenting to an Australian paediatric Emergency 
Department with HIs were enrolled. Published inclusion/exclusion criteria and 
predictor variables from the CDRs were collected prospectively. Using these we 
determined the frequency with which each CDR was applicable.
RESULTS: 1012 patients (69.9%) were enrolled with 949 available for analysis. 
Mean age was 6.8 years (21% <2 years). 95% had initial Glasgow Coma Scale 15. CT 
rate was 12.8% and neurosurgery rate was 0.7%. No CDR was applicable to all 
patients. CHALICE was applicable to the most (97%, 95% CI 96% to 98%) and CATCH 
to the fewest (26%, 95% CI 24% to 29%). PECARN was applicable to 76% (95% CI 70% 
to 82%) aged <2 years, and 74% (95% CI 71% to 77%) aged 2-<18 years.
CONCLUSIONS: Each CDR is applicable to a different proportion of children with 
HI. This makes a direct comparison of the CDRs difficult. Prior to selection of 
any for implementation they should undergo validation outside the derivation 
setting coupled with an analysis of their performance accuracy, usability and 
cost effectiveness.