April MD, Keim SM, Koyfman A, et al. - Researchers aimed at determining the necessity for a subsequent lumbar puncture among patients undergoing evaluation for atraumatic subarachnoid hemorrhage (SAH) who have a negative computed tomography (CT) scan of the head obtained more than 6 hours after symptom onset in order to rule out the diagnosis. The retrieved studies include a retrospective cohort study, two prospective cohort studies, and a case-control study. Emergency clinicians should perform a lumbar puncture, when SAH probability is above 1.0%. This threshold is essentially equivalent to the estimated probability of SAH in patients with a negative head CT retrieved more than 6 hours from symptom onset. Emergency clinicians might reasonably make a decision to either conduct or forego this procedure. The decision whether to conduct lumbar puncture in these instances is an excellent time for shared decision-making.