🧠 Ottawa SAH Rule (Subarachnoid Hemorrhage)
The Ottawa SAH Rule is a high-sensitivity clinical rule to help exclude subarachnoid hemorrhage in alert patients with acute non-traumatic headache.
The rule is designed to be ~100% sensitive at the cost of low specificity — it rules out, it does not rule in, so a positive result is expected in many benign headaches. (original synthesis · not guideline verbatim)
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When to use
Apply only to those meeting entry criteria, then check the six items; any positive item means SAH cannot be excluded and mandates further workup (CT ± LP/CTA).
How it works
Six items: age ≥ 40, neck pain/stiffness, witnessed loss of consciousness, onset during exertion, thunderclap (instantly peaking) headache, limited neck flexion on exam. Rule positive if any item present.
Key points
- The rule is designed to be ~100% sensitive at the cost of low specificity — it rules out, it does not rule in, so a positive result is expected in many benign headaches. (original synthesis · not guideline verbatim)
- Entry criteria are strict: age ≥ 15, new severe atraumatic headache peaking within 1 hour, and a normal neurological exam.
- It does not apply to patients with neurological deficits, prior aneurysm/SAH/brain tumor, or recurrent identical headaches.
References
- Perry JJ, et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA. 2013;310(12):1248-1255.
- Perry JJ, et al. Validation of the Ottawa Subarachnoid Hemorrhage Rule. BMJ. 2020;369:m1224.
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Age ≥ 40 years | Yes |
|---|---|
| Neck pain or stiffness | Present |
| Witnessed loss of consciousness | Present |
| Onset during exertion | Yes |
| Thunderclap headache (instantly peaking) | Yes |
| Limited neck flexion on exam | Present |
→DeterminationCannot exclude — further workup needed
- Positive items：6 / 6
| Age ≥ 40 years | No |
|---|---|
| Neck pain or stiffness | Absent |
| Witnessed loss of consciousness | Absent |
| Onset during exertion | No |
| Thunderclap headache (instantly peaking) | No |
| Limited neck flexion on exam | Absent |
→DeterminationRule negative
- Positive items：0 / 6
Frequently asked questions
- What is Ottawa SAH Rule (Subarachnoid Hemorrhage)?
- The Ottawa SAH Rule is a high-sensitivity clinical rule to help exclude subarachnoid hemorrhage in alert patients with acute non-traumatic headache.
- How is Ottawa SAH Rule (Subarachnoid Hemorrhage) calculated? What is the core formula?
- Six items: age ≥ 40, neck pain/stiffness, witnessed loss of consciousness, onset during exertion, thunderclap (instantly peaking) headache, limited neck flexion on exam. Rule positive if any item present.
- When is Ottawa SAH Rule (Subarachnoid Hemorrhage) used?
- Apply only to those meeting entry criteria, then check the six items; any positive item means SAH cannot be excluded and mandates further workup (CT ± LP/CTA).
- What are the key clinical points for Ottawa SAH Rule (Subarachnoid Hemorrhage)?
- The rule is designed to be ~100% sensitive at the cost of low specificity — it rules out, it does not rule in, so a positive result is expected in many benign headaches. (original synthesis · not guideline verbatim) Entry criteria are strict: age ≥ 15, new severe atraumatic headache peaking within 1 hour, and a normal neurological exam. It does not apply to patients with neurological deficits, prior aneurysm/SAH/brain tumor, or recurrent identical headaches.
- What are the limits and cautions when using Ottawa SAH Rule (Subarachnoid Hemorrhage)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is Ottawa SAH Rule (Subarachnoid Hemorrhage) calculated in practice? Can you show a worked example?
- Inputs: Age ≥ 40 years Yes, Neck pain or stiffness Present, Witnessed loss of consciousness Present, Onset during exertion Yes, Thunderclap headache (instantly peaking) Yes, Limited neck flexion on exam Present → Result: Determination Cannot exclude — further workup needed（Positive items: 6 / 6） Inputs: Age ≥ 40 years No, Neck pain or stiffness Absent, Witnessed loss of consciousness Absent, Onset during exertion No, Thunderclap headache (instantly peaking) No, Limited neck flexion on exam Absent → Result: Determination Rule negative（Positive items: 0 / 6）