P.111 Initial validation of symptom scores derived from the Orthostatic Discriminant and Severity Scale

Background: To develop a scale to quantify and discriminate orthostatic from non-orthostatic symptoms. We present initial validation and reliability of orthostatic and non-orthostatic symptom scores taken from the Orthostatic Discriminate and Severity Scale (ODSS). Methods: Validity and reliability were assessed in participants with and without orthostatic intolerance. Convergent validity was assessed by correlating symptoms scores with previously validated tools (Autonomic Symptom Profile (ASP) and the Orthostatic Hypotension Questionnaire (OHQ)). Clinical validity was assessed by correlating scores against standardized autonomic testing. Test-retest reliability was calculated using an intra-class correlation coefficient. Results:Convergent Validity: Orthostatic (OS) and Non-Orthostatic (NS) Symptom Scores from 77 controls and 67 patients with orthostatic intolerance were highly correlated with both the Orthostatic Intolerance index of the ASP (OS:r=0.903;NS:r=0.651; p<0.001) and the OHQ: (OS:r=0.800;NS:r=0.574; p<0.001). Clinical Validity: Symptom Scores were significantly correlated with the blood pressure change during head-up tilt (OS:r=-0.445;NS:r=-0.354; p<0.001). Patients with orthostatic intolerance had significantly higher symptom scores compared to controls (OS:66.5±18.1 vs. 17.4±12.9; NS:19.9±11.3 vs. 10.2±6.8; p<0.001, respectively). Test-retest reliability: Both symptom scores were highly reliable (OS:r=0.956;NS:r=0.574, respectively; p<0.001) with an internal consistency of 0.978 and 0.729, respectively. Conclusions: Our initial results demonstrate that the ODSS is capable of producing valid and reliable Orthostatic and Non-Orthostatic Symptom Scores.