Foremost among the limitations is to resolve the conundrum of differentiating “euvolemic” patients with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) from hypovolemic patients with cerebral/renal salt wasting (C/RSW) by this ineffectual and technically inaccurate volume approach, as all credible volume determinations in SIADH have shown them to be hypervolemic and not euvolemic [8,9,10,11]. The gene discussed is AVP; the disease is inappropriate ADH syndrome.