Decides whether an adult with minor head injury needs a CT scan, from five high-risk and two medium-risk factors.
Result
Choose the type of head injury, then tick any factor that is present.
Sources
4 studies
4
studies
1,585
citations
124
PubMed papers
Evidence
Known limitations
In 3,121 patients, the five high-risk factors were 100% sensitive (95% CI 92% to 100%) for neurological intervention, and would have required CT in 32%. All seven factors were 98.4% sensitive and 49.6% specific for clinically important brain injury, with CT in 54%.
In 1,822 patients with a GCS of 15, the rule was 100% sensitive for neurosurgical intervention (specificity 76.3%) and for clinically important brain injury (specificity 50.6%); it would have led to CT in 52.1% of patients, against 88.0% for the New Orleans Criteria.
In an external validation in 3,181 Dutch patients, the rule was 100% sensitive for neurosurgical intervention, but less sensitive than the New Orleans Criteria for clinically important CT findings (83.4% to 87.2% against 97.7% to 99.4%).
In a cluster-randomized trial of 4,531 patients at 12 emergency departments, active implementation of the rule did not reduce CT use compared with control sites (CT referral rose at both), and no brain injuries were missed.
CMAJ: Journal Metrics Score 1.5, Q2 · cited 148 times
PubMed · Free full text · DOI
The original paper has been cited 1,585 times, and 124 PubMed articles mention the Canadian CT Head Rule in their title or abstract. Citation counts from OpenAlex and article counts from PubMed, retrieved November 14, 2026. Journal Metrics Scores and quartiles are from this site’s current release; follow the journal name for details.
After the result
CT required · CT not required · Outside the rule
Arrange head CT. Discharge with advice. Clinical judgment.
Next steps
Avoid common errors
5 common errors to avoid
and 3 more
When the rule misleads
1Check eligibility first
The rule is for blunt head injury with loss of consciousness, amnesia or disorientation and a GCS of 13 to 15. It does not cover minimal head injury, children or patients on anticoagulants.
2Syncope and seizures
If the head injury followed a collapse from syncope or a seizure, the rule does not apply; the cause of the collapse needs its own assessment.
3Delayed bleeding
A normal first CT does not exclude a later chronic subdural hematoma, especially in older adults. Discharge advice matters.
4Persistent symptoms
A rule-negative patient with an unexplained, persistent headache or new symptoms still warrants imaging or observation.
5GCS at 2 hours
The GCS factor is assessed 2 hours after the injury; a patient seen earlier may need reassessment before the rule can be applied fully.
Formula
CT is required with any high-risk factor (GCS below 15 at 2 h, open or depressed fracture, basal skull fracture signs, vomiting twice or more, age 65 or older) or medium-risk factor (amnesia 30 minutes or more, dangerous mechanism).
Any factor present: CT required
CT is required with any high-risk factor (GCS below 15 at 2 h, open or depressed fracture, basal skull fracture signs, vomiting twice or more, age 65 or older) or medium-risk factor (amnesia 30 minutes or more, dangerous mechanism).
Risk factors and result
| Factor | Level | Detail |
|---|---|---|
| GCS below 15 at 2 hours after injury | High | Not back to a GCS of 15 two hours after the injury. |
| Suspected open or depressed skull fracture | High | A wound or deformity suggesting an open or depressed fracture. An obvious one is an exclusion: image it directly. |
| Any sign of basal skull fracture | High | Hemotympanum, periorbital bruising (raccoon eyes), CSF leak from the ear or nose, or bruising behind the ear (Battle’s sign). |
| Vomiting, 2 or more episodes | High | Two or more separate episodes after the injury. |
| Age 65 or older | High | 65 years or older (the Lancet abstract prints “>65”, but the rule figure and validation use 65 or older). |
| Amnesia before impact of 30 minutes or more | Medium | Retrograde amnesia: no memory of events for 30 minutes or more before the injury. |
| Dangerous mechanism | Medium | Pedestrian struck by a motor vehicle, occupant ejected from a motor vehicle, or fall from a height of more than 3 feet (0.9 m) or 5 stairs. |
| Result | Meaning |
|---|---|
| CT not required | None of the seven factors is present, so CT is not required by the rule. In the Canadian validation study the rule missed no patient who needed neurosurgery or had a clinically important brain injury; an external validation in the Netherlands found it still identified every patient needing neurosurgery but missed some CT abnormalities. |
| CT required: medium risk | A medium-risk factor is present: these identify patients at risk of a clinically important brain injury on CT, most of whom will not need surgery. CT is required by the rule. |
| CT required: high risk | A high-risk factor is present: these identified every patient in the derivation study who needed neurosurgical intervention. CT is required by the rule. |
| Outside the rule | The Canadian CT Head Rule does not apply to this patient, so it cannot be used to decide on CT. Use clinical judgment and local head injury guidance. |
Stiell 2001
Stiell 2005
Exclusions
Test cases
3 published cases, each also a test case
3 published cases; the calculator reproduces every result.
Worked examples
An 84-year-old man slipped and fell after showering and hit the back of his head on a wall. He was dazed for a moment without losing consciousness, and came in 8 hours later with vomiting and dizziness. His GCS was 15, the neurological examination was normal and he took no antiplatelet or anticoagulant drugs. The author applied the Canadian CT Head Rule: two high-risk features, vomiting and age. CT was normal, but 2 months later he returned with an unsteady gait and a large chronic subdural hematoma, which was drained.
“his Canadian CT Head Rule score included 2 high-risk features of vomiting and age”
Entered as the author scored it. His momentary daze is taken as disorientation (the report does not say it was witnessed); without it he would have had a minimal head injury, outside the rule. The report does not say how many times he vomited. Age 65 or older alone requires CT.
Entered as: Head injury: GCS 13 to 15 with witnessed loss of consciousness, definite amnesia or witnessed disorientation; Any exclusion applies: no; GCS below 15 at 2 hours after injury: no; Suspected open or depressed skull fracture: no; Any sign of basal skull fracture: no; Vomiting, 2 or more episodes: yes; Age 65 or older: yes; Amnesia before impact of 30 minutes or more: no; Dangerous mechanism: no.
Source: Chia MYC, J Am Coll Emerg Physicians Open 2020 (PubMed · Free full text · DOI)
A 30-year-old man felt lightheaded in the bathroom early in the morning, collapsed and lost consciousness for under 5 minutes. On arrival his GCS was 15, the examination was normal and he took no anticoagulants, but he had a persistent headache and nausea. The authors note that CT was not indicated by the usual rules; it was done because of the headache and showed a subarachnoid hemorrhage and a small right frontal contusion; CT angiography showed no aneurysm, and the pattern suggested a contrecoup injury from an occipital impact.
“it represents a “rule-negative” presentation of traumatic SAH”
The authors call this rule-negative, and none of the seven factors appears in the report. But he felt lightheaded and collapsed before hitting his head, and the authors discuss syncope (while calling a vasovagal cause less likely). A collapse with no clear history of trauma as the main event is one of the rule’s exclusions, so we enter it as outside the rule. His loss of consciousness was also not witnessed: he was found on the floor. A persistent, unexplained headache was the reason for CT, and it is a reason to image whatever the rule says.
Entered as: Head injury: GCS 13 to 15 with witnessed loss of consciousness, definite amnesia or witnessed disorientation; Any exclusion applies: yes; GCS below 15 at 2 hours after injury: no; Suspected open or depressed skull fracture: no; Any sign of basal skull fracture: no; Vomiting, 2 or more episodes: no; Age 65 or older: no; Amnesia before impact of 30 minutes or more: no; Dangerous mechanism: no.
Source: Ahmed A et al., Cureus 2025 (PubMed · Free full text · DOI)
A 21-year-old woman hit her head on a table edge and lost consciousness for about 2 minutes, then was confused with headache and double vision. On arrival her GCS was 15, and the examination showed bilateral sixth nerve palsy, which resolved about 20 minutes after it began. She had no vomiting and no signs of basal skull fracture. The authors applied the Canadian CT Head Rule and found no indication for CT, but did a CT because of the palsy: it showed a nondisplaced occipital fracture extending into the petrous bone of the skull base.
“When applying this rule to our case, there was no indication for head CT scan.”
None of the seven factors was present, which is the authors’ reading. But she had an acute focal deficit (the sixth nerve palsy) when examined, and that is one of the rule’s exclusions, so we enter it as outside the rule. A new focal deficit after head injury is a reason for CT in its own right. CT found a fracture through the petrous bone (skull base) even though there were no clinical signs of basal skull fracture.
Entered as: Head injury: GCS 13 to 15 with witnessed loss of consciousness, definite amnesia or witnessed disorientation; Any exclusion applies: yes; GCS below 15 at 2 hours after injury: no; Suspected open or depressed skull fracture: no; Any sign of basal skull fracture: no; Vomiting, 2 or more episodes: no; Age 65 or older: no; Amnesia before impact of 30 minutes or more: no; Dangerous mechanism: no.
Source: Alalwi S et al., Cureus 2021 (PubMed · Free full text · DOI)
FAQ
6 questions and answers
and 4 more answers
Questions
A decision rule for adults with minor head injury, meaning blunt trauma within the previous 24 hours with witnessed loss of consciousness, definite amnesia or witnessed disorientation and a GCS of 13 to 15. CT is required if any of five high-risk or two medium-risk factors is present.
High risk: GCS below 15 two hours after injury, suspected open or depressed skull fracture, any sign of basal skull fracture, vomiting two or more times, and age 65 or older. Medium risk: amnesia for 30 minutes or more before the impact, and a dangerous mechanism (pedestrian struck by a vehicle, ejection from a vehicle, or a fall from more than 3 feet or 5 stairs).
In the derivation study of 3,121 patients the high-risk factors identified every patient who needed neurosurgical intervention. In the validation study, among 1,822 patients with a GCS of 15, the rule was 100% sensitive for neurosurgical intervention and for clinically important brain injury, and would have led to CT in 52% of patients.
Age under 16; on anticoagulants or with a bleeding disorder; a seizure after the injury; an acute focal neurological deficit; unstable vital signs with major trauma; an obvious penetrating skull injury or depressed fracture; no clear history of trauma as the main event (for example a collapse from syncope or a seizure); pregnancy; or a return visit for the same injury. These patients need assessment on clinical grounds; most guidance advises CT for those on anticoagulants, with a seizure or with a focal deficit.
In a direct comparison in patients with a GCS of 15, both rules were 100% sensitive for neurosurgical intervention and clinically important brain injury, but the Canadian rule was far more specific (50.6% vs 12.7% for brain injury), so it would lead to fewer scans (52% vs 88%).
Not necessarily. In a cluster-randomized trial at 12 Canadian emergency departments, CT use rose at both intervention sites (62.8% to 76.2%) and control sites (67.5% to 74.1%), with no significant difference; no brain injuries were missed.
Further reading
7 references with PubMed and DOI links
7
references
4
free full text
From Stiell IG et al., Lancet 2001 to the newest case reports.
References
clinical grade of aneurysmal subarachnoid hemorrhage, I to V.
total calcium adjusted for albumin, in mg/dL or mmol/L.
stroke severity from 15 bedside items, 0 to 42.
MAP from systolic and diastolic pressure, against the 65 mm Hg target.
eye, verbal and motor scores for preverbal children, 3 to 15.
oxygenation ratio with the Berlin ARDS severity ranges.
serum sodium corrected for high glucose, Katz or Hillier factor.
sodium − (chloride + bicarbonate), with the albumin-corrected gap.
urea nitrogen to creatinine ratio, in US or SI units.
estimated creatinine clearance with actual, ideal or adjusted weight.
cardiac output and index from oxygen consumption and saturations.
ANC from the white cell count, neutrophils and bands.
insulin resistance from fasting glucose and insulin, in US or SI units.
FENa from plasma and urine sodium and creatinine: prerenal, indeterminate or tubular pattern.
three-item stroke severity screen for large vessel occlusion, 0 to 4.
water deficit in hypernatremia from sodium, weight and body water.
expected PaCO2 in metabolic acidosis, 1.5 × HCO3 + 8 ± 2.
corrected QT interval by Bazett, Fridericia, Framingham or Hodges.
head CT decision rule for children with minor head trauma.
blood loss before hemoglobin or hematocrit reaches a chosen lowest value.
eye, verbal and motor response, 3 to 15, with GCS-Pupils.
Devine ideal body weight and adjusted weight from height and sex.
cuffed and uncuffed tube size and oral depth by age.
calculated osmolality, osmolal gap and ethanol correction.
severity of alcohol-associated hepatitis from prothrombin time and bilirubin.
MELD, MELD-Na and MELD 3.0 for chronic liver disease.
early stroke risk after a transient ischemic attack.
whether a patient with blunt trauma needs cervical spine imaging.
prognosis from a Bruce protocol exercise test.
alveolar–arterial oxygen gradient from a blood gas.
risk of advanced liver fibrosis from age, AST, ALT and platelets.
Which published the original rule, with its current metrics.
Contributed by Dr. Meng Zhao (MD · Former Neurosurgeon · Medical AI Researcher), from the original publications listed here. Last updated November 14, 2026. LinkedIn
The calculator code is tested against every worked example on this page before each release.
This calculator supports, and does not replace, clinical judgment. It is meant for healthcare professionals and is not medical advice for patients. Report an error through the contact page.