Urinary Retention in Older Adults with Hyponatremia admitted to Acute Medical Wards

Background Hyponatremia and urinary retention are common medical problems. While associations between the two are documented, research has not clearly established the incidence of urinary retention in hyponatremic patients. Objectives To determine the incidence of urinary retention in hyponatremic patients and assess whether urinary catheter insertion affects the sodium correction rate. Methods A prospective, single centre, observational study including patients hospitalized in Internal Medicine and Geriatric wards. A total of 199 older patients (mean age 84.4, 39% men) were investigated: 100 with hyponatremia ≤129 mEq/L (of these, 70 had severe hyponatremia ≤125 mEq/L) and 99 normonatremic controls. The incidence of urinary retention was checked in all groups. Hyponatremic patients underwent complete assessment for the cause of hyponatremia and sodium levels were followed up for 48 hours. Results There was a marked increase in the incidence of urinary retention in older hyponatremic patients compared to those with normal sodium levels (41% vs 21%, p=0.004). The difference was even greater when comparing those with severe hyponatremia to controls (44% vs 21%, p=0.001). Among hyponatremic patients with and without urinary retention, there was no difference in sodium correction rate between the two groups. Patients with polyuria secondary to post-obstructive diuresis had more rapid sodium correction (9.2±6.8 mEq/L vs 5.8±4.8 mEq/L, p=0.05). Conclusions There was a significantly higher incidence of urinary retention in older patients with hyponatremia, which correlates with hyponatremia severity. Post-obstructive diuresis following catheter insertion is associated with more rapid sodium correction. We recommend routine bladder scanning for all patients with hyponatremia.