SUN-306 The Interaction Between Thiazide-Associated Hyponatremia and Acute Illness in Hospitalised Patients

Thiazide diuretics, widely used in the management of hypertension, are associated with a five times greater risk of hyponatremia (serum Na <135mmol/L) than in the general population. Hyponatremia in hospitalised patients warrants special consideration since it is associated with increased morbidity and mortality. The aim of this study was to describe the clinical characteristics and outcomes in acutely ill medical patients with thiazide-associated hyponatremia (TAH). We performed a retrospective, case control study examining all acute, unselected medical admissions, over a six week period, to The Royal London Hospital. Cases were defined as adults admitted to hospital with TAH (hyponatremia and a history of being prescribed thiazide diuretic pre-admission). Each case was matched by age, gender and degree of hyponatremia to a similar control - admitted with hyponatremia and no pre-admission exposure to thiazide (non-TAH). Clinical characteristics and treatment outcomes were compared between TAH and non-TAH cohorts. A total of 1,341 consecutive acute medical admissions (49.7% men) were evaluated. Hyponatremia was detected in 240 (17.9%) admissions. Median (±SD) length of stay was longer among patients with hyponatremia compared to normonatremic patients (5.0±12.4 versus 3.0±9.2 days; p=<0.0001). In-hospital mortality was higher in the hyponatremic group (8.8% versus 4.4% p=0.005). Twenty-two cases (11 men) of TAH accounted for 9.2% of patients with hyponatremia. Median age 64±14 years was similar to other patients with hyponatremia 68±20 years. The median admission serum sodium for TAH cases was 131.5 mmol/L (IQR 126.8 - 134) with a discharge serum sodium of 136.5 mmol/L (IQR 133.8 - 139.3). When compared to matched controls, patients with TAH had similar presenting symptoms - most commonly confusion, headache and dizziness. Length of stay among TAH cases was similar to controls; 5.5±5.1 versus 4.0±3.7 days; p=0.24. Mortality (10%) was the same in both groups. Thiazide was withdrawn during admission in 14 (64%) cases. In conclusion, acute, clinical outcomes for hospitalised patients with TAH are similar to those with comparable degrees of hyponatremia due to other causes.