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

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 (n = 137) 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 (n = 113) 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 without headache and in patients presenting >6 hours after ictus, CSF analysis is still indicated. (Stroke. 2012; 43: 2115-2119.)