Interactive Ottawa SAH (Subarachnoid Hemorrhage) Rule calculator. Requires the calculator gadget. Usage: {{Ottawa SAH Calculator}}
Ottawa SAH Rule
Ottawa SAH Rule — SAH Risk in Acute Headache
| Inclusion: alert patients >15 years old with new severe non-traumatic headache reaching maximum intensity within 1 hour. Not for patients with new neurologic deficits, prior aneurysm/SAH, known brain tumor, or chronic recurrent headaches (≥3 episodes over ≥6 months).
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| Criterion
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No
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Yes
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| Age ≥40 years
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1
|
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| Neck pain or stiffness
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1
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| Witnessed loss of consciousness
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1
|
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| Onset during exertion
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1
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| Thunderclap headache (instantaneous peak intensity)
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1
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| Limited neck flexion on exam
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1
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| Criteria Present
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/ 6
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| Interpretation
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| 0 of 6
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SAH effectively ruled out — 100% sensitivity in validation study. Further investigation for SAH not required based on this rule alone; consider alternative headache etiologies.
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| ≥1 of 6
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SAH NOT ruled out — rule does not rule in SAH; proceed with non-contrast CT head (within 6 hours of onset is most sensitive) ± lumbar puncture if CT negative and clinical suspicion remains.
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| References
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- Perry JJ, Stiell IG, Sivilotti MLA, et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA. 2013;310(12):1248-1255. PMID 24065011.
- Perry JJ, Sivilotti MLA, Sutherland J, et al. Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache. CMAJ. 2017;189(45):E1379-E1385. PMID 29133539.
- Sensitivity: 100% (95% CI 94.6–100); Specificity: ~13–15% — high sensitivity tool intended to identify patients who do NOT need further SAH workup.
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