Subarachnoid haemorrhage rules in the decision for acute CT of the head: external validation in a UK cohort.

Background: The Ottawa subarachnoid haemorrhage (SAH) rule and the Emerald SAH rule are clinical decision tools to aid in the decision for computed tomography (CT) of the head in patients attending an emergency department (ED) with acute non-traumatic headache. The objective of this study was to analyse the performance of these rules in a contemporary UK cohort.

Methods: We performed a retrospective external validation study.