Table 3

 Sensitivity of computed tomography for subarachnoid haemorrhage in patients with acute headache stratified by timing of scan

Time from headache onset to scanNo of patients% Sensitivity (95% CI)% Specificity (95% CI)Likelihood ratio (95% CI)Predictive value (95% CI)
Positive NegativePositive Negative
All patients313292.9 (89.0 to 95.5)100 (99.9 to 100)Infinity0.07 (0.05 to 0.11)100 (98.3 to 100)99.4 (99.1 to 99.6)
≤6 hours953100 (97.0 to 100.0)100 (99.5 to 100)Infinity0.00 (0.00 to 0.02)100 (96.9 to 100)100 (99.5 to 100)
>6 hours217985.7 (78.3 to 90.9)100 (99.8 to 100)Infinity0.14 (0.14 to 0.17)100 (96.3 to 100)99.2 (98.7 to 99.5)