• Dustin G Mark, Yun-Yi Hung, Steven R Offerman, Adina S Rauchwerger, Mary E Reed, Uli Chettipally, David R Vinson, Dustin W Ballard, and Kaiser Permanente CREST Network Investigators.
• Department of Emergency Medicine, Kaiser Permanente, Oakland, CA, USA. dustin.g.mark@kp.org
• Ann Emerg Med. 2013 Jul 1;62(1):1-10.e1.

Study ObjectiveClinical variables can reliably exclude a diagnosis of nontraumatic subarachnoid hemorrhage in patients with negative cranial computed tomography (CT) results. We externally validated 2 decision rules with 100% reported sensitivity for a diagnosis of subarachnoid hemorrhage, among patients undergoing lumbar puncture after a negative cranial CT result: (1) clinical rule: presence of any combination of age 40 years and older, neck pain or stiffness, loss of consciousness, or headache onset during exertion; and (2) imaging rule: cranial CT performed within 6 hours of headache onset.MethodsThis was a matched case-control study of patients presenting to 21 emergency departments between 2000 and 2011. Patients with a diagnosis of subarachnoid hemorrhage as determined by lumbar puncture after a negative cranial CT result were screened for inclusion. A matched control cohort was selected among patients with a diagnosis of headache after negative cranial CT and lumbar puncture results.ResultsFifty-five cases of subarachnoid hemorrhage meeting inclusion criteria were identified, 34 (62%) of which were attributed to cerebral aneurysms. External validation of the clinical rule demonstrated a sensitivity of 97.1% (95% confidence interval [CI] 88.6% to 99.7%), a specificity of 22.7% (95% CI 16.6% to 29.8%), and a negative likelihood ratio of 0.13 (95% CI 0.03 to 0.61) for a diagnosis of subarachnoid hemorrhage. External validation of the imaging rule revealed that 11 of 55 subarachnoid hemorrhage cases (20%) had negative cranial CT results for tests performed within 6 hours of headache onset.ConclusionThe clinical rule demonstrated useful Bayesian test characteristics when retrospectively validated against this patient cohort. The imaging rule, however, failed to identify 20% of subarachnoid hemorrhage patients with a negative cranial CT result.Copyright © 2012 American College of Emergency Physicians. Published by Mosby, Inc. All rights reserved.

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