CT is often unavailable in a rural setting, and additional transport may be necessary with the risk and expense that goes with a decision for CT. The Canadian CT Head Rules help with this decision in a setting of minor head injury, defined as Glasgow Coma Scale 13 -15. Although other decision paths exist, these rules at present have the best evidence in terms of external validation. In fact, by 2 hours post-injury, these rules pertain only to GCS 15 patients.
Because the Canadian CT Head Rules included only patients with loss of consciousness and memory loss, and because they excluded patients with seizures, coagulopathy and abnormal neurologic findings, the CHIP prediction rules have been recently developed to include such patients. These rules still need external validation.
Additional features of the history and exam are sometimes considered in more at-risk medicolegal climates such as the USA. Some consideration must be given to broadening of CT indications in such environments.