35 y F presents to ED with sudden onset worst headache of life starting 3 hours ago.  Refractory to treatment with excedrin.  No history of Migraines.  Concern for SAH. What is your management algorithm to rule out SAH?  Do you CT/LP?

While traditional emergency medicine teaching has dictated LP if CT is negative, it is probably time to rethink that dogma.  Two recent studies indicate that with 3rd generation CT scanners, performing a head CT within the first 6 hours of symptom onset has a negative predictive value of 100% for SAH.  While these studies were performed in tertiary care, academic centers it turns out that these results also apply to community hospitals as well as a recent study in the Netherlands indicates which showed a negative predictive value of 99.9%.  Additionally, there is a significant amount of false positives on LP (around 15% in the Netherlands study were false positives and up to 1/3 have been shown to be false positives previously).  The effects of false positives should not be undersold – this can lead to further, unnecessary radiation exposure and possibly repeat LPs, which have their own side effects (infection, HA, etc.).   There is probably sufficient data to change practice at this point, but don’t take my word for it; for more information check out the links below.

Check out this article from our very own, Dr. David Newman, who was on this several years ago:


Review of the Netherlands study: