CT only rule-out of subarachnoid hemorrhage?

Can a CT read within 6 hours of headache onset can rule out SAH without the need for a lumbar puncture? This study found a 99% NPV of staff-read CTs in 11 non-academic centers with a 1/15,200 missed aneurysmal SAH. This study did not discuss the accuracy of resident or emergency medicine interpretations of CT scans. 

A multicenter, retrospective study of 11 non-academic centers. Included patients older than 16, with acute-onset headache of known duration without focal deficits or altered mental status. To be included, patients had to undergo a CT in <6 hours from headache onset and a lumbar puncture >12 hours from headache onset. 760 patients were included with 52 positive CSF findings. On review of CT imaging, 51 were considered negative, and only one perimesencephalic nonaneurysmal SAH was found, and no readmissions due to SAH. 

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