Background:Orthostatic symptoms including dizziness, light-headedness and syncope can be major causes of disability in patients with dysautonomia. Currently there is no validated tool capable of discriminating orthostatic from non-orthostatic constitutional symptoms. Therefore, we developed the Orthostatic Discriminant and Severity Scale (ODSS) to help make this distinction. Objective: Demonstrate validity and reliability of the ODSS.Methods:Convergent and clinical validity were assessed by

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... elating Orthostatic scores with previously validated tools (Autonomic Symptom Profile (ASP), composite scores of the Orthostatic Hypotension Questionnaire and the total Composite Autonomic Severity Score (tCASS), respectively). Test-retest reliability was calculated using an intra-class correlation coefficient.Results:Orthostatic scores from 23 controls and 5 patients were highly correlated with both the Orthostatic Intolerance index of the ASP (r=0.724;p<0.01) and the composite OHDAS and OHSAS (r=0.552;p<0.01 and r=0.753;p<0.01, respectively), indicating good convergent validity. Orthostatic scores were significantly correlated with tCASS (r=0.568;p<0.01), and the systolic blood pressure change during head-up tilt (r=-0.472;p=0.013). In addition, patients with Neurogenic Orthostatic Hypotension had significantly higher Orthostatic scores than controls (p<0.01) indicating good clinical validity. Test-retest reliability was strong (r=0.954;p<0.01) with an internal consistency of 0.978.Conclusions:Our results, though preliminary, provide empiral evidence that the ODSS is capable of producing a valid and reliable orthostatic score.