Migraine vs. thunderclap headache – red flags in the ED?

One caveat: if CT was within 6h and is negative, sensitivity for SAH is ~98%. Some centers skip LP in that scenario. Discuss with neurology and document the shared decision.

The phrase 'worst headache of my life' with thunderclap onset mandates LP or CTA regardless of migraine history. CT sensitivity for SAH drops after 6h. Don't anchor on the migraine history.

Ottawa SAH rule is useful here — if onset was truly sudden and maximal at onset, LP is warranted even with negative CT. Xanthochromia in CSF is your answer.