Canadian CT Head Rule
Need for head CT after minor head injury (GCS 13–15) in adults
Sources last checked: 2026-10-13
Canadian CT Head Rule
Need for head CT after minor head injury (GCS 13–15) in adults
Patients on anticoagulants, with bleeding disorders, seizures or age < 16 were excluded from the derivation, so the rule says nothing about them. Clinical judgement and local guidance (e.g. NICE NG232, which adapts these criteria) take precedence.
Interpretation
| Rule not applicable | The patient is outside the population the rule was derived in, so the rule makes no statement about imaging for this patient. |
|---|---|
| CT not required by the rule | No high- or medium-risk factor. In the derivation the rule missed no patient needing neurosurgical intervention and was 98.4 % sensitive for clinically important brain injury. |
| CT indicated by the rule — medium risk | Medium-risk factor present: risk of clinically important brain injury on CT. |
| CT indicated by the rule — high risk | High-risk factor present: risk of needing neurosurgical intervention. |
What is the Canadian CT Head Rule?
The Canadian CT Head Rule identifies adults with minor head injury who need a CT scan. Stiell and colleagues derived it in 2001 from 3,121 patients with GCS 13–15 after head injury in ten Canadian emergency departments. Five high-risk factors predict the need for neurosurgical intervention and two medium-risk factors predict clinically important brain injury.
When to use it
- Adults (≥ 16 years) with GCS 13–15 after head injury and witnessed loss of consciousness, definite amnesia or witnessed disorientation.
- Reducing unnecessary CT in low-risk minor head injury.
- Structuring documentation of CT decisions in the emergency department.
When not to use it
- Patients on anticoagulants or with bleeding disorders.
- Children under 16 — use paediatric rules such as PECARN or CATCH.
- Post-traumatic seizures, obvious penetrating or depressed skull injuries, focal deficits or unstable vital signs.
How it is calculated
Applies to: age ≥ 16, GCS 13–15 after head injury with witnessed loss of consciousness, definite amnesia or witnessed disorientation. CT if ANY high-risk factor (GCS < 15 at 2 h; suspected open/depressed fracture; sign of basal skull fracture; vomiting ≥ 2; age ≥ 65) or ANY medium-risk factor (amnesia before impact > 30 min; dangerous mechanism). Otherwise no CT by the rule.
Clinical pearls and limitations
- Patients on anticoagulants, with bleeding disorders, seizures or age < 16 were excluded from the derivation, so the rule says nothing about them. Clinical judgement and local guidance (e.g. NICE NG232, which adapts these criteria) take precedence.
- The rule only applies to patients with loss of consciousness, amnesia or disorientation; minimal head injury without these was not studied.
- Dangerous mechanism: pedestrian struck by a vehicle, ejection from a vehicle, or fall from ≥ 3 feet (about 1 m) or 5 stairs.
- NICE NG232 adapts the same risk factors (e.g. > 1 vomiting episode, age ≥ 65, retrograde amnesia > 30 min).
- Age ≥ 65 alone is a high-risk factor in this rule.
Frequently asked questions
Who needs a CT after a minor head injury?
Under this rule, any patient with a high-risk factor (GCS < 15 at 2 h, suspected open/depressed or basal skull fracture, vomiting ≥ 2, age ≥ 65) or a medium-risk factor (amnesia > 30 min before impact, dangerous mechanism).
Does the rule apply to patients on anticoagulants?
No. They were excluded from the derivation; local guidance usually sets a low threshold for CT.
How sensitive is the Canadian CT Head Rule?
In derivation, 100 % for need of neurosurgical intervention (high-risk factors) and 98.4 % for clinically important brain injury (all factors).
Evidence and guidelines
- Primary source: 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 — recommendations 1.5.8–1.5.9 and 1.6.1–1.6.3 (criteria adapted from the Canadian rules).
Have a follow-up question?
Medelix answers clinical questions from current guidelines and studies — every statement with its source.
Ask Medelix about the Canadian CT Head RuleRelated calculators
Embed this calculatorFree to use on your website, intranet or teaching page. Copy the code below.
<iframe src="https://medelix.ai/en/embed/canadian-ct-head" title="Canadian CT Head Rule – Medelix" width="100%" height="620" style="border:0;max-width:720px" loading="lazy"></iframe>
<p><a href="https://medelix.ai/en/calculators/canadian-ct-head-rule">Canadian CT Head Rule calculator by Medelix</a></p>For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.