Approach to the patient with suspected hypotonic polyuria

Investigation and management of hypotonic polyuria is a common challenge in clinical endocrinology. The 3 main causes, recently renamed to arginine vasopressin deficiency (AVP-D, formerly central diabetes insipidus), arginine vasopressin resistance (AVP-R, formerly nephrogenic diabetes insipidus), and primary polydipsia (PP) require accurate diagnosis, as management differs for each. This new nomenclature more accurately reflects pathophysiology and has now been adopted by the Systemized Nomenclature of Medicine (SNOMED). Advances in diagnosis over the last few years have centered around the use of copeptin measurement. Here, we use 3 patient case histories to highlight the use of this approach, and to demonstrate how it can succeed where other approaches, such as the water deprivation test, sometimes fail. We discuss the overall approach to each type of patient and the strengths and limitations of diagnostic strategies, illustrating the use of the new nomenclature.