A

A non-contrast head CT is the first test because thunderclap “worst headache of life” raises concern for subarachnoid hemorrhage, and immediate CT rapidly identifies most cases and guides whether further testing (e.g., lumbar puncture) is needed [Abraham & Chang, 2016, PMID 27741994; Cohen-Gadol & Bohnstedt, 2013, PMID 24134085].