About the Canadian CT Head Rule
The Canadian CT Head Rule is a validated clinical decision rule that helps emergency clinicians decide which adults with a minor head injury need a CT scan of the head. It was derived by Stiell and colleagues in 3,121 patients at ten Canadian emergency departments and published in The Lancet in 2001. It identifies five high-risk factors that predict the need for neurosurgical intervention and two medium-risk factors that predict clinically important brain injury on CT.
The rule applies only to patients aged 16 or over with a minor head injury — a Glasgow Coma Scale (GCS) of 13–15 together with witnessed loss of consciousness, definite amnesia or witnessed disorientation. It does not apply to patients taking anticoagulants or with a bleeding disorder, or to those with an obvious penetrating skull injury or depressed fracture, an acute focal neurological deficit, a seizure after the injury, unstable vital signs, pregnancy, or a return visit for the same injury; in those groups imaging decisions are made on clinical grounds.
Tick each criterion that applies. If any factor is present the rule is positive and recommends CT; if none is present, the rule indicates CT is not required. In the derivation study the high-risk factors were 100% sensitive for injuries needing neurosurgery, and all seven factors were 98.4% sensitive for clinically important brain injury; in the 2005 validation study of 2,707 patients the rule was 100% sensitive for both outcomes. The rule supports — never replaces — clinical judgement.
How to use the canadian ct head rule
- 1Confirm the patient has a minor head injury: GCS 13–15 with witnessed LOC, definite amnesia or witnessed disorientation.
- 2Check for exclusions such as age under 16, anticoagulants or a seizure after the injury.
- 3Tick any of the five high-risk factors.
- 4Tick either medium-risk factor if present.
- 5Read the result: any factor makes the rule positive; none makes it negative.
Formula and method
The rule is a simple checklist, not a weighted score. The five high-risk factors were selected because they identified every patient in the derivation cohort who needed neurosurgical intervention. The two medium-risk factors were added to capture clinically important brain injury on CT that may not need surgery but still requires admission or follow-up.
If any one of the seven factors is present the rule is positive. In the 2001 Lancet derivation study (3,121 patients) the high-risk factors had 100% sensitivity (95% CI 92–100%) for neurosurgical intervention and would have required CT in only 32% of patients; all seven factors had 98.4% sensitivity (95% CI 96–99%) and 49.6% specificity for clinically important brain injury, requiring CT in 54%. In the 2005 JAMA validation (2,707 patients with GCS 13–15) sensitivity was 100% for both outcomes.
- GCS
- Glasgow Coma Scale score (3–15)
- Dangerous mechanism
- Pedestrian struck by vehicle, ejection from vehicle, or fall > 3 ft or 5 stairs
Worked examples
Young adult with no risk factors
A 30-year-old with a brief witnessed loss of consciousness, GCS 15 and none of the seven risk factors. The rule is negative, so CT is not required by the rule.
Older patient after a fall
A 72-year-old who fell down a flight of stairs has one high-risk factor (age ≥ 65) and one medium-risk factor (fall from more than 5 stairs). The high-risk factor alone makes the rule positive.
Cyclist with long pre-impact amnesia
No high-risk factors are present, but the patient cannot remember the 45 minutes before the crash. Retrograde amnesia over 30 minutes is a medium-risk factor, so the rule recommends CT.
Patient on an anticoagulant
Anticoagulant use was an exclusion in the original study, so the rule cannot be used to decide about imaging; local guidance and clinical judgement apply instead.
Frequently asked questions
Who does the Canadian CT Head Rule apply to?+
Adults aged 16 or older with a minor head injury, defined as a GCS of 13–15 after witnessed loss of consciousness, definite amnesia or witnessed disorientation. It excludes patients on anticoagulants, with bleeding disorders, seizures, focal deficits, obvious penetrating or depressed skull injuries, unstable vital signs or pregnancy, and injuries more than 24 hours old.
What counts as a dangerous mechanism?+
In the Canadian CT Head Rule a dangerous mechanism is a pedestrian struck by a motor vehicle, an occupant ejected from a motor vehicle, or a fall from a height of more than 3 feet (about 0.9 m) or more than five stairs.
What are the signs of a basal skull fracture?+
Signs include haemotympanum (blood behind the eardrum), periorbital bruising (“raccoon eyes”), cerebrospinal fluid leaking from the ear or nose, and bruising behind the ear over the mastoid (Battle’s sign).
How does it compare with the New Orleans Criteria?+
In a 2005 JAMA head-to-head study of 1,822 patients with GCS 15, both rules were 100% sensitive for neurosurgical intervention, but the Canadian CT Head Rule was far more specific (76.3% vs 12.1%) and would have led to fewer CT scans (52.1% vs 88.0% for clinically important brain injury).
Can the rule be used in children?+
No. It was derived and validated only in patients aged 16 and over. For children, separate rules such as PECARN, CATCH or CHALICE are used to guide imaging after head injury.
For healthcare professionals and education only. This calculator implements a published formula or score but is not a diagnosis and does not replace clinical judgment. Verify inputs and results against the original source before using them in patient care.
Sources
- Stiell IG et al. The Canadian CT Head Rule for patients with minor head injury. Lancet 2001;357:1391–6 (PubMed)
- Stiell IG et al. A prospective cluster-randomized trial to implement the Canadian CT Head Rule. CMAJ 2010 (PMC)
- Stiell IG et al. Comparison of the Canadian CT Head Rule and the New Orleans Criteria. JAMA 2005 (PubMed)