Emergency Medicine
Canadian CT Head Rule
Whether CT is needed after minor head injury.
Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.
Background
The Canadian CT Head Rule is a clinical decision rule that identifies which adults with minor head injury require a CT scan, allowing imaging to be safely avoided in low-risk patients. It applies to minor head injury defined as a Glasgow Coma Scale (GCS) of 13–15 with witnessed loss of consciousness, amnesia or disorientation. It comprises five high-risk criteria (GCS <15 at 2 hours, suspected open or depressed skull fracture, any sign of basal skull fracture, ≥2 episodes of vomiting, and age ≥65) and two medium-risk criteria (retrograde amnesia ≥30 minutes and a dangerous mechanism of injury). If any criterion is present, CT is indicated.
Interpreting the result
If no criteria are present, the rule indicates that a CT head is not required and the patient can usually be observed and discharged with safety-net advice. The presence of one or more criteria means CT is indicated. The high-risk criteria predict the need for neurosurgical intervention, while the medium-risk criteria predict clinically important brain injury on CT.
Worked example
A 68-year-old presents after a fall with a GCS of 15 and no other features except age ≥65. Because age ≥65 is a high-risk criterion, one criterion is present, so a CT head is indicated despite an otherwise reassuring examination.
Critical actions
Applies only to minor head injury meeting the inclusion criteria. It does NOT apply to patients on anticoagulants, with bleeding disorders, or post-seizure — image per local policy.
Pearls / pitfalls
- The rule applies only to minor head injury meeting the inclusion criteria — it does not apply to patients on anticoagulants or with bleeding disorders, who should be imaged per local policy.
- It excludes those under 16, post-seizure presentations, unstable vital signs and obvious penetrating trauma.
- A dangerous mechanism includes pedestrian struck by a vehicle, ejection, or a fall from height (more than about 3 feet or 5 stairs).
- Clinical judgement and safety-netting remain essential; the rule supports, but does not replace, assessment.
Evidence & validation
Derived and validated by Stiell and colleagues in large Canadian emergency-department cohorts, where it was highly sensitive for injuries needing neurosurgical intervention. It is endorsed in NICE head-injury guidance, which incorporates the same high-risk features into its CT criteria.
Frequently asked questions
Can the Canadian CT Head Rule be used in anticoagulated patients?
No. The rule was derived in patients without coagulopathy and excludes those on anticoagulants or with bleeding disorders. Such patients should be considered for CT according to local guidance regardless of the rule.
What GCS range does it cover?
It applies to minor head injury with a GCS of 13–15 and a history of loss of consciousness, amnesia or disorientation. Patients with a lower GCS fall outside the rule and need urgent imaging.
Does no criteria being present guarantee there is no bleed?
No clinical rule is perfect, but the rule is highly sensitive for clinically important injury. With no criteria present, CT can generally be safely avoided, accompanied by observation and clear safety-net advice.
What is a dangerous mechanism?
Examples include being a pedestrian struck by a motor vehicle, ejection from a vehicle, or a fall from a height greater than about 3 feet or 5 stairs. A dangerous mechanism is a medium-risk criterion that prompts CT.
References
- Stiell IG, Wells GA, Vandemheen K, et al. The Canadian CT Head Rule for patients with minor head injury. Lancet. 2001;357(9266):1391–1396.
- NICE NG232: Head injury: assessment and early management. 2023.
About the creator
Stiell IG et al.
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