Hyponatremia and Urinary Retention: Cause, Effect, or Coincidence?

Background: Hyponatremia is the most common electrolyte disorder, with an incidence up to 10% of patients admitted to the emergency room (ER). There are few reports about urinary retention in context of hyponatremia. In our hospital the protocol of hyponatremia evaluation and treatment includes an urinary catheter insertion for follow up of urinary output. Methods: This is a retrospective analysis of clinical and laboratory data of all adult (>18 years old) patients admitted to ER of our hospital during 2021 with moderate and severe hyponatremia (<130 meql/L) and/or urinary retention. Patients were identified based on the lab data at the time of ER admission or diagnoses in electronic records. Results: Total of 190 cases in hyponatremia group and 214 cases in urinary retention group included. In hyponatremic group average age was 83.8 years (24-99), most of them were females (72.6%), 30% with diabetes mellitus. Forty two percent of patients received chronic diuretic therapy, while 22% of them received more than one type of diuretic. Almost 56% of patients received different benzodiazepines, or antidepressants, anticonvulsants or anti-psychotics. In 37.4% of cases severe hyponatremia (<120 meq/L) was observed. An urinary catheter was inserted in 104 cases; in 54 of them urinary retention of more than 300 ml was recorded. Patients in the catheter group had a tendency to more severe hyponatremia (57% of them were with sodium <120 meq/L vs 9% in patients without urinary catheter insertion), and there was a trend to more prolonged hospital stay (median 5 days vs 2). Three months all-cause mortality was observed in almost 19%, while mortality was higher in patients without urinary retention (42% vs 17%, p<0.0001). In Urinary retention group only in 10 patients (4.7%) had moderate hyponatremia while only in one patient severe hyponatremia was found. Conclusion: Elderly women have higher incidence of moderate to severe hyponatremia than men. Since 3 months all-cause mortality is high in these patients, probably hyponatremia is a sign of more serious prognosis, especially in absence of urinary retention. Our data suggest that urinary retention per se does not lead to hyponatremia. It is therefore reasonable to assume that urinary retention appears to develop secondary to hyponatremia, rather than etiologically linked.