Ottawa SAH Rule
Clinical decision rule to identify patients with acute non-traumatic headache who require investigation for subarachnoid haemorrhage. 100% sensitivity in derivation and validation studies.
Inclusion Criteria
ALL must be met before applying the Ottawa SAH Rule
Age 15 years or older
The rule has not been validated in paediatric populations.
New severe non-traumatic headache
Must be a new headache pattern, not chronic or recurrent. Trauma-related headache is excluded.
Reaching maximum intensity within 1 hour
Rapid-onset headache is the hallmark of SAH. Headaches building over days are less concerning for SAH.
Alert (GCS 15)
Patients with reduced GCS need urgent investigation regardless of the Ottawa rule.
Neurologically intact
Focal neurological deficits mandate investigation irrespective of decision rules.
Based on Perry JJ et al. BMJ2013;347:f4585 (Ottawa SAH Rule derivation & validation). Enhanced with clinical pearls by Dr Sumit Mandal. For educational purposes only — always use clinical judgement.