(HealthDay News) – For patients presenting to the emergency department with headache peaking within one hour and no neurologic deficits, the Ottawa Subarachnoid Hemorrhage Rule is highly sensitive for identifying subarachnoid hemorrhage, according to a study published in the Sept. 25 issue of the Journal of the American Medical Association.

Jeffrey J. Perry, MD, from the University of Ottawa in Canada, and colleagues evaluated the accuracy, reliability, acceptability, and potential refinement of three clinical decision rules previously derived to identify patients with headache requiring investigations to rule out subarachnoid hemorrhage. The multicenter cohort study was conducted at 10 emergency departments from April 2006–July 2010 and included 2,131 adults with a headache peaking within one hour and no neurologic defects.

The researchers found that 6.2% of the enrolled patients had subarachnoid hemorrhage. The sensitivity and specificity for subarachnoid hemorrhage were 98.5% and 27.5%, respectively, for the decision rule including one or more of the following: age 40 years or older, neck pain or stiffness, witnessed loss of consciousness, or onset during exertion. Adding the criteria of thunderclap headache and limited neck flexion on examination (the Ottawa Subarachnoid Hemorrhage Rule) resulted in sensitivity and specificity of 100% and 15.3%, respectively.

“These findings apply only to patients with these specific clinical characteristics and require additional evaluation in implementation studies before the rule is applied in routine clinical care,” the authors write.

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