AVP and neurohypophyseal diabetes insipidus: Differential diagnoses for polyuria include diabetes mellitus (osmotic diuresis), hypokalemia and hypercalcemia (secondary arginine vasopressin resistance), hyperthyroidism (increased renal plasma flow), urinary tract infections (increased frequency that may be misinterpreted as polyuria), and disorders of water balance such as primary polydipsia (washout of renal medullary gradient), arginine vasopressin deficiency (central diabetes insipidus), and arginine vasopressin resistance (nephrogenic diabetes insipidus).1,4,9-11