Research in context
Evidence before this study
We searched PubMed with no language restrictions for papers published from database inception up to July 6, 2020, to include prehospital prospective validation studies of prehospital stroke scales. We used the search terms “prehospital triage”, “prehospital stroke scale”, “large vessel occlusion”, and “mechanical thrombectomy” or “endovascular therapy”, and we cross-checked references of eligible papers. Many prehospital stroke scales have been developed, but prospective prehospital validation studies are scarce. We identified nine studies validating prehospital stroke scales in the field. None of these studies validated multiple scales simultaneously and most were done in small or selected populations, limiting the generalisability of their results.
Added value of this study
To the best of our knowledge, our study is the first to validate eight prehospital stroke scales simultaneously in a large population of individuals with suspected stroke by paramedics in the field using a mobile app. Our study provided reliable estimates of the in-field performance of eight prehospital stroke scales. CT angiographies were done in hospital and reassessed by an Imaging Core Laboratory committee to validate the true occlusion status.
Implications of all the available evidence
Prehospital stroke scales are helpful to guide prehospital selection of people with suspected stroke. In general, prehospital stroke scales detect large-vessel occlusions well and the different scales perform similarly. The best in our study were Rapid Arterial oCclusion Evaluation (RACE), Gaze-Face-Arm-Speech-Time (G-FAST), and Conveniently-Grasped Field Assessment Stroke Triage (CG-FAST), which approached the performance of the clinician-assessed National Institutes of Health Stroke Scale (NIHSS). However, due to its complexity, NIHSS is not the ideal scale for assessment by paramedics in the field. Our finding that a field-assessed RACE score of 5 or higher corresponds to a 40% or higher risk of large-vessel occlusion in the anterior circulation (positive predictive value 0·40) supports implementation of RACE (or another prehospital stroke scale with a similar threshold) in clinical practice in most urban and suburban regions. However, in rural areas with longer driving times to the intervention centre, higher positive predictive value thresholds should be considered. With our study evidence, health-care professionals and policy makers might be able to better decide on the most suitable prehospital stroke scale and threshold to customise prehospital triage to regional characteristics, such as distribution of hospitals and their stroke treatment capabilities, population density, and regional workflow times.