Background::Vasovagal syncope (VVS) greatly impairs quality of life. The therapeutic efficacy of oral rehydration saline (ORS) for unselected VVS patients is not satisfactory due to the diverse mechanisms of the disease. Body mass index (BMI) was demonstrated to reflect blood volume to a certain extent. Therefore, the present study explored the capability of BMI to predict the therapeutic response of children with VVS to ORS treatment.Methods::Seventy-four children with VVS who visited the Syncope Unit of Pediatrics at Peking University First Hospital from November 2010 to June 2019 receiving ORS treatment were enrolled for this retrospective case-control study. A comparison of demographic, clinical, and hemodynamic characteristics was performed between responders and non-responders. The correlation between baseline BMI and response time was analyzed. To determine the value of baseline BMI in predicting the therapeutic efficacy of ORS in children with VVS, a receiver operating characteristic curve analysis was performed.Results::Fifty-two children were identified as responders, and the remaining 22 children were identified as non-responders. The baseline BMI of the responders was much lower than that of the non-responders (16.4 [15.5, 17.8] kg/mn 2vs. 20.7 ± 3.6 kg/mn 2, n P < 0.001), and baseline BMI was positively correlated with response time in the head-up tilt test after adjusting for sex ( n r = 0.256, 95% confidence interval [CI]: 0.067-0.439, n P = 0.029). The area under the receiver operating characteristic curve of baseline BMI was 0.818 (95% CI: 0.704-0.932, n P < 0.001), and an optimal cut-off value of 18.9 kg/m n 2 yielded a sensitivity of 83% and a specificity of 73% to predict the efficacy of ORS in VVS.n Conclusion::Prior to treatment, baseline BMI is a promising predictor of response to ORS in children with VVS.“,”Background::Vasovagal syncope (VVS) greatly impairs quality of life. The therapeutic efficacy of oral rehydration saline (ORS) for unselected VVS patients is not satisfactory due to the diverse mechanisms of the disease. Body mass index (BMI) was demonstrated to reflect blood volume to a certain extent. Therefore, the present study explored the capability of BMI to predict the therapeutic response of children with VVS to ORS treatment.Methods::Seventy-four children with VVS who visited the Syncope Unit of Pediatrics at Peking University First Hospital from November 2010 to June 2019 receiving ORS treatment were enrolled for this retrospective case-control study. A comparison of demographic, clinical, and hemodynamic characteristics was performed between responders and non-responders. The correlation between baseline BMI and response time was analyzed. To determine the value of baseline BMI in predicting the therapeutic efficacy of ORS in children with VVS, a receiver operating characteristic curve analysis was performed.Results::Fifty-two children were identified as responders, and the remaining 22 children were identified as non-responders. The baseline BMI of the responders was much lower than that of the non-responders (16.4 [15.5, 17.8] kg/mn 2vs. 20.7 ± 3.6 kg/mn 2, n P < 0.001), and baseline BMI was positively correlated with response time in the head-up tilt test after adjusting for sex ( n r = 0.256, 95% confidence interval [CI]: 0.067-0.439, n P = 0.029). The area under the receiver operating characteristic curve of baseline BMI was 0.818 (95% CI: 0.704-0.932, n P < 0.001), and an optimal cut-off value of 18.9 kg/m n 2 yielded a sensitivity of 83% and a specificity of 73% to predict the efficacy of ORS in VVS.n Conclusion::Prior to treatment, baseline BMI is a promising predictor of response to ORS in children with VVS.