encephalopathy; furosemide; hyponatremia; registry; risk; sodium; Thiazide; thiazide-induced hyponatremia (TIH); thiazideassocitated hyponatremia (TAH); uric acid; water-excretion

Objectives: Thiazide-associated hyponatremia (TAH) is a clinically important side effect of the therapy with thiazide and thiazide-like diuretics. This study aims to analyze epidemiological, biochemical, and symptomatological profiles (including volume status) of patients admitted with TAH. Methods: A retrospective hospital record study was performed. Epidemiological and biochemical parameters and symptoms were compared between the thiazide (n = 143) and non-thiazide (n = 282) groups. Patients in the thiazide group were classified as hypo-, normo-, or hypervolemic. Furthermore, the comparison of epidemiological, biochemical, partially pharmacotherapeutical, and symptomatological parameters between the hypovolemic and normovolemic TAH groups was performed. Results: The thiazide group showed lower s-Na (p = 0.008), s-K (p < 0.001), s-CI (p < 0.001), measured s-osmolality (p = 0.021), and eGFR (p < 0.001); higher s-urea (p < 0.001), s-creatinine (p = 0.023), s-glucose (p < 0.001), u-osmolality (p = 0.012), u-Na (p < 0.001), u-K (p = 0.023), and u-CI (p < 0.001). Patients using thiazide were older (p < 0.001), more likely to be female (p = 0.011), and with symptoms corresponding more to chronic hyponatremia. Compared to the normovolemic group (n = 93; 65%), the hypovolemic patients (n = 47; 32.9%) showed higher s-urea (p = 0.005), s-creatinine (p = 0.045), and s-UA (p = 0.010); lower eGFR (p = 0.032), u-Na (p = 0.015), u-CI (p = 0.016), anorexia (p < 0.001), and a higher frequency of furosemide use (p < 0.001). Conclusions: Thiazide use is a crucial etiological cause of hypotonic hyponatremia among internal medicine inpatients, associated with more severe hyponatremia, but with no difference in the inhospital mortality. Even in hypo-osmolar conditions of TAH, 32.9% of patients exhibited signs of volume depletion. FE-UA did not differ between the hypovolemic and the normovolemic patients in TAH conditions.