Association of hyponatremia with increased renin activity in chronic congestive heart failure: impact of diuretic therapy.

A correlation between hyponatremia and increased plasma renin activity (PRA) has been reported in patients with severe congestive heart failure (CHF), implying both clinical and pathophysiologic significance. To determine the impact of diuretic therapy on this relation, we evaluated the correlation of serum sodium, prerenal azotemia (blood urea nitrogen/creatinine ratio [BUN/Cr] ), and PRA in 44 patients with severe CHF who were maintained on diuretic therapy. Serum sodium level was inversely related to PRA (r = -0.389, p less than 0.02). However, a significant correlation also existed between the BUN/Cr ratio and PRA (r = 0.365, p less than 0.025) and an inverse correlation between serum sodium level and the BUN/Cr ratio (r = 0.332, p less than 0.025). Multiple regression analysis of the 3 variables yielded significant interdependence (p less than 0.01). To evaluate the effect of diuretic therapy, 12 patients with severe CHF discontinued diuretic therapy and received, for 1 week each, 10 and 100 mEq sodium diets in balance studies. PRA ranged from 0.14 to 16 ng/ml/h. Despite this range, there was no significant correlation between either serum sodium or BUN/Cr ratio and PRA. It is concluded that the presence of marked hyponatremia and prerenal azotemia in patients with diuretic-treated CHF may suggest increased PRA. However, substantial patient-to-patient variability limits the predictive value of these correlations. Although some clinical value may be derived from such correlations, they should not be used to draw major inferences regarding the severity of CHF or the pathophysiology of water balance in CHF.