AVP and nephrolithiasis: There is potential misclassification of variables inherent to administrative data which relies heavily on diagnosis codes entered by individual hospital personnel. Because IBS is not always reported, or diagnosed, the overall data may be incomplete or exposed to bias. Therefore, this exploratory study and analysis may be skewed. Additionally, the lack of ICD-9 coding for plasma osmolality, and perhaps the sheer lack of testing, prevent this study from confirming the hypothesis of plasma osmolality and copeptin levels as a link to nephrolithiasis risk and stone formation.