Canadian CT Head Rule Calculator
For minor head injury with GCS 13–15, five high-risk and two medium-risk criteria decide who needs a CT. Know the exclusions cold — the rule does NOT apply to anticoagulated patients, which is exactly where neurology gets consulted.
Reviewed by Zaka Ahmed, MD Clinical reference · 4 min read
Canadian CT Head Rule
Apply only if ALL entry criteria are met: blunt head trauma with witnessed loss of consciousness, amnesia, or witnessed disorientation; GCS 13–15 at assessment; injury within 24 hours. Do NOT apply if any exclusion below is present.
The recommendation appears here once all items are answered.
Educational tool only. The rule was derived for minor head injury meeting strict entry criteria; outside them — anticoagulation above all — it provides no reassurance and imaging decisions default to clinical judgment (which, on anticoagulants, nearly always means CT). It does not replace in-person evaluation.
Clinical notes & interpretation Scoring guidance, pitfalls, FAQs, and references
A rule that works — inside its fence
Stiell's derivation (3,121 patients) and subsequent validations showed the five high-risk criteria capture essentially all minor-head-injury patients who need neurosurgical intervention, and the two medium-risk criteria capture clinically important CT findings. Used as designed, it cuts imaging substantially without missing operative lesions. Everything depends on the entry criteria and exclusions: GCS 13–15, injury under 24 hours, actual LOC/amnesia/disorientation — and no anticoagulation, no post-injury seizure, no focal deficit, age 16 or older.
The exclusion that matters most to a stroke practice
Anticoagulated head trauma is the collision point between stroke prevention and trauma, and it sits explicitly outside this rule. The working defaults: image essentially every anticoagulated patient with head trauma regardless of how minor it looks; remember delayed intracranial hemorrhage occurs (mostly reported on warfarin — risk on DOACs appears lower, but observation advice and repeat-imaging protocols vary locally); and treat a confirmed traumatic ICH on anticoagulation as a reversal decision (PCC for warfarin, idarucizumab for dabigatran, andexanet or PCC for Xa inhibitors per local protocol) followed later by the harder question — when, and whether, to resume anticoagulation. That resumption conversation is CHA₂DS₂-VASc versus rebleed risk, and it belongs to exactly the clinic this site serves.
Frequently asked questions.
Does the rule apply to patients on aspirin or clopidogrel?
Antiplatelet agents were not an exclusion in the original derivation (anticoagulants and bleeding disorders were). Many clinicians nonetheless image antiplatelet patients liberally, particularly on dual therapy or with age ≥65 — which usually triggers a criterion anyway.
Canadian CT Head Rule or New Orleans Criteria?
Head-to-head, both were highly sensitive but the Canadian rule was substantially more specific — fewer scans for the same safety. New Orleans applies only to GCS 15.
What counts as a dangerous mechanism?
Pedestrian struck by a vehicle, occupant ejected from a vehicle, or a fall from more than 3 feet or 5 stairs.
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. PubMed
- Stiell IG, Clement CM, Rowe BH, et al. Comparison of the Canadian CT Head Rule and the New Orleans Criteria in patients with minor head injury. JAMA. 2005;294(12):1511–1518. PubMed