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Printed on 6/29/2026
For informational purposes only. This is not medical advice.
The Canadian CT Head Rule identifies patients with minor head injury (GCS 13–15) who require CT scanning. It uses high-risk criteria (for neurosurgical intervention) and medium-risk criteria (for brain injury on CT) to safely reduce unnecessary imaging while maintaining near-100% sensitivity for significant findings. Formally score GCS with [Glasgow Coma Scale Calculator](/tools/glasgow-coma-scale). For concurrent cervical spine clearance decisions, apply [NEXUS C-Spine Rule](/tools/nexus-c-spine). Assess stroke or neurological deficit with [NIHSS Calculator](/tools/nihss). For intubated or ICU patients, quantify severity with [APACHE II](/tools/apache-ii).
Formula: Decision rule with 4 high-risk and 2 medium-risk criteria. Any positive criterion = CT recommended.
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The Canadian CT Head Rule applies ONLY to patients with minor head injury (GCS 13–15) AND at least one of: witnessed loss of consciousness, definite amnesia, or witnessed disorientation. Do NOT apply to patients with GCS <13, penetrating injury, active anticoagulation, coagulopathy, post-seizure, or children under 16 — these patients require CT regardless.
Assess for any high-risk criterion: (1) GCS <15 at 2 hours post-injury; (2) suspected open or depressed skull fracture; (3) any sign of basal skull fracture (raccoon eyes, Battle's sign, hemotympanum, CSF rhinorrhea/otorrhea); (4) vomiting ≥2 separate episodes; (5) age ≥65 years. Any single criterion = CT recommended for neurosurgical intervention risk.
If all high-risk criteria are absent, assess medium-risk: (1) amnesia before impact ≥30 minutes; (2) dangerous mechanism (pedestrian struck by motor vehicle, ejected from vehicle, fall from >3 feet or >5 stairs, high-energy MVC). Any medium-risk criterion = CT recommended to detect brain injury on imaging even if neurosurgical intervention is unlikely.
Emergency physicians
The Canadian CT Head Rule is primarily used in emergency departments to determine whether CT head is needed after minor head injury. It has 100% sensitivity for neurosurgical lesions and 98.4% sensitivity for brain injury, allowing safe deferral of CT in lower-risk patients and reducing unnecessary radiation exposure and healthcare costs.
Emergency physicians, hospital administrators
Implementing the Canadian CT Head Rule as a formal clinical protocol can reduce CT utilization in eligible patients by 30–40% compared to indiscriminate imaging. This reduces radiation exposure, contrast use, scanner wait times, and healthcare costs without compromising the detection of clinically significant injuries.
Emergency physicians, neurosurgeons
High-risk criteria (GCS <15 at 2h, skull fracture, 2+ vomiting, age ≥65) identify patients at risk for neurosurgically significant injuries requiring neurosurgical consultation. The rule has 100% sensitivity for these lesions in the original derivation cohort.
Emergency physicians, geriatricians
Age ≥65 alone qualifies for CT under the high-risk criteria — even with GCS 15 and minimal mechanism. Elderly patients have higher risk of intracranial hemorrhage from seemingly minor falls due to cerebral atrophy (larger subdural space), antiplatelet use, and falls from standing height.
All emergency physicians
Documenting application of the Canadian CT Head Rule provides objective, validated clinical decision support for triage decisions in minor head injury. This structured approach demonstrates evidence-based practice in both appropriate CT ordering and safe deferral decisions.
The rule has strict inclusion criteria: GCS must be 13–15 AND the patient must have witnessed LOC, definite amnesia, or witnessed disorientation. GCS <13 = CT always (no rule needed). Patients without any cognitive disturbance after head trauma are not eligible for the rule.
Patients on warfarin, heparin, DOACs (rivaroxaban, apixaban, dabigatran, edoxaban), or with coagulopathy were excluded from the derivation study. Most centers have a lower CT threshold for anticoagulated patients with any head trauma, even minor. Do not use the Canadian CT Head Rule to defer CT in anticoagulated patients.
The high-risk age criterion (≥65) means that any eligible elderly patient with minor head injury qualifies for CT based on age alone, regardless of mechanism severity. Elderly patients have cerebral atrophy expanding the subdural space, higher antiplatelet use, and lower bone density — all increasing intracranial hemorrhage risk with minimal trauma.
Basal skull fracture signs: periorbital ecchymosis ('raccoon eyes'), retroauricular ecchymosis ('Battle's sign' — appears 24–48 hours after injury), hemotympanum (blood behind tympanic membrane on otoscopy), CSF rhinorrhea (clear fluid from nose that may test positive for beta-2 transferrin), CSF otorrhea (clear fluid from ear). Any of these = high-risk criterion = CT.
The high-risk GCS criterion is GCS <15 at 2 hours post-injury, not at ED presentation. A patient who arrives with GCS 14 but improves to GCS 15 by 2 hours is negative for this criterion. Conversely, a patient with GCS 15 at arrival who deteriorates to GCS 14 at 2 hours is positive. Serial neurological assessment is essential.
Dangerous mechanism criteria: pedestrian or cyclist struck by motor vehicle; occupant ejected from motor vehicle; fall from height >3 feet (1 meter) or >5 stairs. Simple standing-height falls in ambulatory adults do NOT constitute dangerous mechanism (though age ≥65 would still qualify for CT). High-velocity MVC or motorcycle accident typically qualifies.
The NEXUS Head CT Rule (Mower et al.) is an alternative clinical decision rule for head CT in blunt trauma. It uses different criteria and was derived from a US population. The Canadian rule has better specificity (lower CT rate) for the same sensitivity. Use whichever tool your institution has adopted and validated in your local population.
The Canadian CT Head Rule was not validated in children under 16. Use PECARN (Pediatric Emergency Care Applied Research Network) head CT rule for children — it uses different variables including altered mental status, scalp hematoma location, loss of consciousness duration, and mechanism. PECARN identifies 'very low risk' children where CT can be deferred with high safety.
Canadian CT Head Rule published by Stiell et al. (Lancet 2001) from 3121 adult patients with minor head injury. High-risk factors: 100% sensitivity for neurosurgical intervention. Medium-risk factors: 98.4% sensitivity for brain injury. External validation by Stiell et al. (JAMA 2005) confirmed sensitivity for clinically important brain injury. Multiple subsequent validations. NEXUS Head CT Rule (Mower et al., Ann Emerg Med 2005) is an alternative tool. ACR Appropriateness Criteria for head trauma reference structured decision tools.
The Canadian CT Head Rule provides a binary recommendation: CT is indicated or CT is not required. If any of the four high-risk criteria are positive (GCS below 15 at 2 hours post-injury, suspected open or depressed skull fracture, two or more episodes of vomiting, or age 65 or older), a CT scan is recommended to evaluate for findings that may require neurosurgical intervention. The high-risk criteria have 100% sensitivity for neurosurgical lesions in the original validation study.
If no high-risk criteria are present but one or both medium-risk criteria are positive (retrograde amnesia exceeding 30 minutes, dangerous mechanism of injury), CT is also recommended to detect brain injuries visible on imaging even if they do not require surgery. If all criteria are negative, the probability of a clinically important brain injury is extremely low, and CT can be safely deferred, reducing unnecessary radiation exposure and healthcare costs.
Use the Canadian CT Head Rule for adult patients (age 16 and older) who present to the emergency department with a minor head injury, defined as witnessed loss of consciousness, definite amnesia, or witnessed disorientation in a patient with a Glasgow Coma Scale score of 13-15. The rule is designed to reduce the rate of unnecessary CT scans in this large patient population while maintaining near-perfect sensitivity for clinically significant injuries.
The rule should NOT be applied to patients with penetrating injuries, patients on anticoagulant therapy or with bleeding disorders, patients with obvious open skull fractures, patients who had a seizure after the injury, or patients with GCS below 13. These patients require CT regardless of the rule's criteria. The rule is also not validated for children under 16, for whom separate pediatric decision rules (PECARN, CATCH, CHALICE) should be used.
The Canadian CT Head Rule was derived and validated in Canadian emergency departments and may have different performance characteristics in other settings. Some validation studies have shown lower specificity than the original study, meaning the rule may still recommend CT for a substantial proportion of patients who do not have significant findings.
The definition of 'dangerous mechanism' is somewhat subjective (pedestrian struck by motor vehicle, occupant ejected from vehicle, fall from height greater than 3 feet or 5 stairs), and clinical judgment is needed in borderline cases. The rule also does not account for patients on antiplatelet agents (only anticoagulants are excluded), despite growing evidence that antiplatelet therapy may increase intracranial bleeding risk. Many clinicians have a lower threshold for imaging in elderly patients on antiplatelets. Finally, the rule addresses the need for imaging at a single time point and does not eliminate the need for clinical re-evaluation if symptoms worsen.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
April 21, 2026 · trust-baseline
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Calculate the Glasgow Coma Scale score to assess level of consciousness. Used worldwide in emergency medicine and trauma assessment.
OpenNeurologyCalculate the NIH Stroke Scale (NIHSS) to quantify stroke severity. Mild ≤4, Moderate 5–15, Severe 16–20, Very Severe >20. Guides IV tPA eligibility and acute stroke unit treatment decisions.
OpenApplies to patients with GCS 13–15, witnessed LOC, amnesia, or disorientation.
High-Risk Criteria:
Medium-Risk Criteria: