Time-Dependent Test Characteristics of Head Computed Tomography in Patients Suspected of Nontraumatic

Background and Purpose—A recent study suggested that in patients with acute headache suspicious of nontraumatic subarachnoid hemorrhage (SAH), cerebrospinal fluid (CSF) analysis is not needed to rule out SAH if head CT performed 6 hours after ictus is negative. Before implementation in daily practice, these results need replication. Therefore, we investigated test characteristics of head CT in patients with a clinical suspicion of SAH. Methods—Patients suspicious of SAH and a normal level of consciousness presenting to our tertiary care hospital between 2005 and 2012 were included. All patients had a head CT interpreted by experienced neuroradiologists and CSF spectrophotometry if head CT was negative or inconclusive. We determined test characteristics with 95 % confidence intervals (CI) for nontraumatic SAH of head CT performed 6 or 6 hours after onset of headache. Results—Sensitivity of head CT 6 hours after ictus (n137) was 98.5 % (95 % CI, 92.1%–100%), diagnosing all patients with aneurysmal and perimesencephalic SAH, but not with a cervical arteriovenous malformation. Sensitivity of head CT performed 6 hours after ictus (n113) was 90.0 % (95 % CI, 76.3–97.2). After exclusion of patients with an atypical presentation without headache, sensitivity, specificity, negative predictive value, and positive predictive value of head CT 6 hours were all 100%. Conclusions—In patients presenting with acute headache and a normal head CT 6 hours after ictus, as interpreted by experienced neuroradiologists, there is no added value of CSF analysis. In patients with an atypical presentation withou