“…At first glance, apparently not all that well -with visual inspection having 83% sensitivity, and for spectrophotometry 87-93% sensitivity. [17][18][19] However, as Bishop points out, it is imperative to consider the pre-test probability of SAH in patients who end up needing a LP, which is around 1% in those who are CT negative. 27 Now both alternatives look rather good, as with a clear 'negative' visual inspection the post-test probability of SAH has dropped to 0.18% (or less than 1 in 500), and with negative spectrophotometry the post-test probability at worst is a mere 0.15%, and at best 0.07% (or less than 1 in a thousand).…”