A prospective study of patients with lung cancer and hyponatremia of malignancy.

This study was undertaken to define the impact of arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) on sodium homeostasis in patients with lung cancer. Patients had their serum and urine electrolytes and osmolality determined before and after a saline infusion of 500 ml. The plasma hormones, AVP, ANP, plasma renin activity (PRA), angiotensin II, and aldosterone were determined by radioimmunoassay every 15 min before, during and after the saline infusion. Fifty patients, 31 with small cell lung cancer and 19 with non-small cell lung cancer participated in this trial. All 11 patients (10 patients with small cell lung cancer and one patient with non-small cell lung cancer) who presented with hyponatremia had inappropriately elevated levels of AVP. Elevated plasma AVP levels were highly correlated with the presence of hyponatremia (p < 0.00001). Initial plasma ANP levels were not associated with hyponatremia (p = 0.73). Urinary sodium concentration increased during the saline infusion proportional to the initial plasma level of ANP (p = 0.0045). AVP appears to be elevated in nearly all patients with hyponatremia of malignancy. ANP plasma levels in patients with lung cancer are associated with the ability to excrete a sodium load but do not appear to downregulate renin, angiotensin II, and aldosterone production.