Review of the Ottawa Subarachnoid Hemorrhage Rule

The Ottawa Subarachnoid Hemorrhage (SAH) Rule is a validated clinical decision tool used to identify SAH in patients who present to the emergency department with acute nontraumatic headache. It aims to reduce missed diagnoses while minimizing unnecessary imaging and invasive testing (e.g., lumbar puncture, CTA, digital subtraction angiography). The rule applies to alert patients (GCS of 15) aged ≥15 years with a new severe headache that peaks within one hour; further investigation is warranted if any of the following high-risk features are present: age ≥40 years, neck pain or stiffness, witnessed loss of consciousness, onset during exertion, thunderclap headache, or limited neck flexion on examination. Exclusion criteria include head trauma within the past 7 days and the presence of any new neurological deficits. While most validation studies demonstrate 100% sensitivity, specificity is relatively low. Thus, this rule should only be used to rule out SAH, not to confirm or diagnose it.