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Introduction: Inter-hospital transfer of ischemic stroke patients by Helicopter Emergency Medical Services (HEMS) is common in rural states. The administration of recombinant tissue plasminogen activator (rtPA) is often initiated at the outside hospital and continues during HEMS (drip and ship). Due to the unstable nature of rtPA after reconstitution in conjunction with strong, low frequency vibrations present during HEMS, there is potential for the physical integrity and thrombolytic activity of rtPA to be compromised during inter-hospital transfer.Hypothesis: Air ambulance transfer alters the antigen integrity of rtPA in ischemic stroke patients.Methods: Prospective cohort study of acute ischemic stroke patients receiving rtPA during air ambulance transfer to a comprehensive stroke center (CSC) (intervention group) compared to patients who presented directly to our CSC Emergency Department (control group). The duration of each flight was recorded to control for degree of exposure. To access the structural integrity and thrombolytic activity of rtPA, small residual samples (<0.5 mL) were taken from each patient’s vial after the infusion was completed. The structural integrity of rtPA antigen was evaluated with a specific rtPA protein ELISA.Results: Thirteen patients received rtPA and were transferred to our CSC via our air ambulance service. The mean flight time was 30.6±5.5 minutes. The mean concentration of rtPA in the control sample was 1.035±0.42 mg/mL. The mean difference in the concentration of the rtPA in the intervention group compared to the control group was 1.59±1.28 mg/mL.Conclusions: HEMS transfer appears to increase rtPA antigen concentrations possibly due to degradation. Future analysis will examine whether alteration in integrity of rtPA affects the thrombolytic activity.