Canadian CT Head Rule Calculator

Canadian CT Head Rule Calculator for Neurology. Unknown two-hour GCS prevents a negative result, but other positive criteria must not prompt waiting. ACEP cautions against using decision tools to exclude CT with anticoagulation or antiplatelet therapy other than aspirin alone: https://www.acep.org/siteassets/new-pdfs/clinical-policies/mtbi2023.pdf

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

Either a high-risk or medium-risk finding indicates CT in an eligible patient. The original derivation is https://pubmed.ncbi.nlm.nih.gov/11356436/ . Exact criteria here follow the 2005 validation Box 2, including age >=65, vomiting >=2 and amnesia >=30 minutes: https://www.mcgill.ca/files/emergency/CT_head_compare.pdf

When to use this calculator

Minor head injury with loss of consciousness, definite amnesia or disorientation, not every head bump. A clinician must confirm the listed exclusions.

Inputs used

  • Eligible minor blunt head injury within 24 hours, initial GCS 13-15, LOC/amnesia/disorientation and no exclusions
  • Age in years
  • GCS at two hours: 15, below 15 or unknown
  • Suspected open/depressed skull fracture
  • Basal skull fracture signs
  • Integer number of vomiting episodes
  • Retrograde amnesia in minutes
  • Dangerous mechanism using the head-rule definition

Clinical interpretation

Unknown two-hour GCS prevents a negative result, but other positive criteria must not prompt waiting. ACEP cautions against using decision tools to exclude CT with anticoagulation or antiplatelet therapy other than aspirin alone: https://www.acep.org/siteassets/new-pdfs/clinical-policies/mtbi2023.pdf

Worked example

Age 40, GCS 15 at two hours, no fracture signs, no vomiting and exactly 30 minutes of pre-impact amnesia meets a medium-risk criterion. CT is indicated by the validated rule.

Limitations and safety notes

The 2001 abstract and later tables use inconsistent comparator shorthand; this version is explicitly pinned to the 2005 validation table. A negative rule is neither discharge clearance nor permission to ignore worsening symptoms.

Frequently asked questions

Is 30 minutes of amnesia below the cutoff?

No. Box 2 of the 2005 validation uses 30 or more minutes. The calculation does not round duration before classification.

References

  • Stiell et al. Original Canadian CT Head Rule, 2001: https://pubmed.ncbi.nlm.nih.gov/11356436/
  • Stiell et al. Prospective validation, JAMA 2005, Box 2 and eligibility: https://www.mcgill.ca/files/emergency/CT_head_compare.pdf
  • ACEP mild TBI clinical policy, 2023; anticoagulant/antiplatelet exclusions: https://www.acep.org/siteassets/new-pdfs/clinical-policies/mtbi2023.pdf

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 9, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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