What is the Canadian CT Head Rule?

The Canadian CT Head Rule is a validated clinical decision rule that helps clinicians determine whether a CT scan of the head is needed in adults with minor head injury (GCS 13–15). It was developed to reduce unnecessary CT scans while identifying patients who need imaging. A patient requires CT if any of the high-risk or medium-risk criteria are met.

When should I use the Canadian CT Head Rule?

Use it for adults (age 16+) with a witnessed loss of consciousness, definite amnesia, or witnessed disorientation after blunt head trauma, who have a Glasgow Coma Scale (GCS) score of 13–15. Do not use it for patients under 16, non-trauma cases, GCS less than 13, bleeding disorders, anticoagulant use, or obvious open skull fractures.

Canadian CT Head Rule Calculator

Apply this rule ONLY if ALL of the following are true: Age ≥ 16 years. Blunt head trauma with witnessed loss of consciousness, definite amnesia, or witnessed disorientation. GCS 13–15 at assessment. Injury within 24 hours.

Do NOT use if: Age < 16. GCS < 13. No witnessed LOC/amnesia/disorientation. Penetrating skull injury. Obvious open or depressed skull fracture. On anticoagulants (warfarin, DOACs) or known bleeding disorder. Returned for reassessment of same injury.

HIGH RISK — CT required (for neurosurgical intervention)

GCS < 15 at 2 hours after injury

Glasgow Coma Scale not returned to 15 within 2 hours of head injury

Suspected open or depressed skull fracture

Palpable depressed fracture, visible bone, or wound penetrating skull

Any sign of basal skull fracture

Haemotympanum, raccoon eyes, CSF otorrhoea/rhinorrhoea, Battle's sign

≥ 2 episodes of vomiting

Two or more distinct episodes of vomiting after the head injury

Age ≥ 65 years

MEDIUM RISK — CT required (for brain injury on CT)

Amnesia before impact > 30 minutes

Retrograde amnesia — patient cannot recall events for more than 30 minutes before the injury

Dangerous mechanism of injury

Pedestrian struck by vehicle, ejected from vehicle, fall from height > 1 metre (5 stairs)

The Canadian CT Head Rule was developed by Ian Stiell and colleagues at the Ottawa Hospital Research Institute. Published in The Lancet in 2001, it was derived from a prospective cohort study of 3,121 patients and subsequently validated.

The rule is designed to identify patients with minor head injury who are at risk of clinically important brain injury requiring neurosurgical intervention (high-risk criteria) or any brain injury visible on CT (medium-risk criteria).

Sensitivity: 100% for neurosurgical intervention, 98.4% for clinically important brain injury. The original derivation study projected a 25–50% relative reduction in CT scan rates; real-world implementation studies since have shown mixed results, with some sites seeing little to no reduction in practice.

Reference: 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. Verified September 2026.

Eye Opening: Spontaneous = 4, To voice = 3, To pain = 2, None = 1

Verbal Response: Oriented = 5, Confused = 4, Inappropriate words = 3, Incomprehensible = 2, None = 1

Motor Response: Obeys commands = 6, Localises pain = 5, Withdrawal = 4, Flexion = 3, Extension = 2, None = 1

Total: 3–15. Minor head injury = GCS 13–15. Moderate = 9–12. Severe = 3–8.

The Canadian CT Head Rule does NOT apply to patients on anticoagulants. Patients taking warfarin, DOACs (apixaban, rivarelbane, dabigatran, edoxaban), or with known bleeding disorders should have a lower threshold for CT head imaging regardless of other criteria.

Many guidelines recommend CT for all anticoagulated patients with head trauma, even if GCS 15 and no other high-risk features, due to the increased risk of delayed intracranial haemorrhage. Consider a period of observation (4–8 hours) even with a normal initial CT in anticoagulated patients.

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