Presence of variable increases likelihood of subarachnoid hemorrhage | Positive likelihood ratio |
Neck stiffness (flexion/extension) on examination | 5.94 |
Loss of consciousness, witnessed | 4.59 |
Loss of consciousness, not witnessed | 3.77 |
Absence of variable decreases likelihood of subarachnoid hemorrhage | Negative likelihood ratio |
Worst headache of life | 0.31 |
Complaint of neck stiffness or pain | 0.42 |
Arrival by ambulance | 0.52 |
↵* Ratios were derived from a study by Perry et al.1 This prospective study excluded patients whose headache began more than 14 days before presentation, as well as patients with recurrent headaches (> three), focal neurologic deficits, papilledema, history of subarachnoid hemorrhage, aneurysm, hydrocephalus or brain neoplasm.