los angeles prehospital stroke screen los angeles prehospital stroke screen the los angeles prehospital stroke screen (abbreviated lapss) is a method of identifying potential stroke patients in a pre-hospital setting. los angeles prehospital stroke screen (lapss)synonymslapsspurposeidentifying potential stroke patients screening criteria no history of seizures or epilepsy age 45 years or older at baseline, patient is not bedridden and does not use a wheelchair blood glucose between 60 and 400 mg/dl obvious asymmetry-unilateral weakness with any of the following motor exams: facial smile/grimace grip arm strength if all of the above criteria are met (or not ascertainable) the lapss is positive for stroke. patients may still be experiencing a stroke even if lapss criteria are not met. validity a january 2000 study, conducted by 3 teams of los angeles-based paramedic units resulted in "sensitivity of 91% (95% ci, 76% to 98%), specificity of 97% (95% ci, 93% to 99%), positive predictive value of 86% (95% ci, 70% to 95%), and negative predictive value of 98% (95% ci, 95% to 99%). with correction for the 4 documentation errors, positive predictive value increased to 97% (95% ci, 84% to 99%)." in a chinese study, beijing paramedics using the protocol, completed lapss screenings in an average of 4.3±3.0 minutes (median, 5 minutes). the study resulted in a sensitivity of 78.44% and a specificity of 90.22%.