Serum sodium concentration and plasma renin activity in CAPD patients.

Hyponatremia is not uncommon in patients on CAPD, despite the presence of an intraabdominal solution that should preserve normal serum sodium concentration. We have examined the relationship between the plasma renin level and serum sodium concentration in our CAPD patients. Patients with abnormal causes for increased thirst were removed from the study; that is, diabetic patients with fluctuating blood sugar or patients on tricyclic antidepressants or clonidine. In forty-one patients a statistically significant inverse correlation between serum sodium and plasma renin levels was demonstrated. We conclude that thirst stimulation by the renin-angiotensin system contributes to the hyponatremia seen in many patients on CAPD.