Canadian CT Head Rule Calculator

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GCS 15 at 2 hours post-injury
If GCS <15 at 2 hours, CT is indicated regardless — do not apply this rule

Suspected open or depressed skull fracture
HIGH RISK — CT required

Any sign of basal skull fracture (raccoon eyes, Battle's sign, haemotympanum, CSF otorrhoea/rhinorrhoea)
HIGH RISK — CT required

≥2 episodes of vomiting
HIGH RISK — CT required

Age ≥65 years
HIGH RISK — CT required

Retrograde amnesia ≥30 minutes before impact
MEDIUM RISK — CT recommended

Dangerous mechanism of injury
MEDIUM RISK — pedestrian struck, occupant ejected, fall >3 feet or >5 stairs

✓ when to use

Apply to adults (≥16 years) with minor head injury: GCS 13–15, witnessed loss of consciousness, definite amnesia, or witnessed disorientation. The patient must have GCS 15 at the time of assessment. If any high-risk or medium-risk criterion is met, CT is indicated.

✗ when not to use

Do NOT apply if: GCS <13, penetrating injury, obvious depressed skull fracture, acute focal neurological deficit, unstable vital signs, seizure after injury, bleeding disorder or anticoagulant use, returned for reassessment after initial injury. These patients need CT imaging regardless. Not validated in children (use PECARN). Not for trivial head injuries with no LOC, amnesia, or disorientation.

clinical pearls

The NICE head injury guideline (CG176) is based heavily on the Canadian CT Head Rule but adds important UK-specific criteria including anticoagulant/antiplatelet use, which automatically mandates CT. Always check the NICE guideline if practising in the UK.
High-risk criteria (suspected skull fracture, basal skull fracture signs, ≥2 vomits, age ≥65) are 100% sensitive for neurosurgical intervention — if none are present, the patient will not need neurosurgery.
Medium-risk criteria (amnesia >30 min, dangerous mechanism) identify additional patients with clinically important brain injuries that don't require surgery but need hospital observation.
Anticoagulation is NOT in the original Canadian CT Head Rule but IS in the NICE guideline. Any patient on anticoagulants (warfarin, DOACs) with head injury should have CT regardless of other criteria.
The rule requires GCS 15 at the time of assessment. A GCS of 14 already warrants CT without applying the rule. Similarly, any focal neurological deficit mandates imaging.

✓ when to use

✗ when not to use

clinical pearls

The NICE head injury guideline (CG176) is based heavily on the Canadian CT Head Rule but adds important UK-specific criteria including anticoagulant/antiplatelet use, which automatically mandates CT. Always check the NICE guideline if practising in the UK.
High-risk criteria (suspected skull fracture, basal skull fracture signs, ≥2 vomits, age ≥65) are 100% sensitive for neurosurgical intervention — if none are present, the patient will not need neurosurgery.
Medium-risk criteria (amnesia >30 min, dangerous mechanism) identify additional patients with clinically important brain injuries that don't require surgery but need hospital observation.
Anticoagulation is NOT in the original Canadian CT Head Rule but IS in the NICE guideline. Any patient on anticoagulants (warfarin, DOACs) with head injury should have CT regardless of other criteria.
The rule requires GCS 15 at the time of assessment. A GCS of 14 already warrants CT without applying the rule. Similarly, any focal neurological deficit mandates imaging.

Canadian CT Head Rule

inputs

✓ when to use

✗ when not to use

clinical pearls

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