Ottawa SAH Rule

Perry JJ, Stiell IG, Sivilotti MLA, et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. Derived and internally validated the Ottawa SAH Rule in alert patients ≥ 15 years with peak headache within 1 hour and no neurological deficit; the six-item rule was 100% sensitive for SAH.

Perry JJ, Sivilotti MLA, Sutherland J, et al. Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache. Prospective multicentre validation: sensitivity 100% (95% CI 94.6–100%) with specificity ~13.6%, confirming the rule identifies patients who need investigation but does not by itself reduce imaging substantially.

Use only within the strict inclusion criteria. A positive rule means SAH cannot be excluded clinically and warrants non-contrast CT (and, depending on timing and pretest probability, lumbar puncture or CT angiography); it does not diagnose SAH.