AVP and Hyponatremia: Hyponatremia is the most common body fluid and electrolyte disorder in clinical practice, which is defined as an excess of water in the extracellular fluid and serum sodium<135 mmol/L.[8] The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is the most prevalent cause of hyponatremia.[9] SIADH was first reported in patients of bronchogenic carcinoma with inappropriate secretion of the arginine vasopressin (AVP).[10] The secretion of AVP is independent of plasma osmolality and is one of the most important pathogenesis of patients with SIADH.