Clinical characteristics at baseline.

Group 1: Normonatremia (initial serum sodium ≥135 mmol/L and stayed normal during admission); Group 2: Corrected hyponatremia (initial serum sodium <135 mmol/L with subsequent normalization during admission, i.e. ≥135 mmol/L); Group 3: Acquired hyponatremia (initial serum sodium ≥135 mmol/L, with subsequent fall during admission to <135 mmol/L); Group 4: Persistent hyponatremia (initial serum sodium <135 mmol/L and stayed <135 mmol/L during admission).
Estimated GFR = 186×([SCR/88.4]−1.154)×(age)−0.203×(0.742 if female), where estimated GFR = estimated glomerular filtration rate (ml/min/1.73 m2), SCR = serum creatinine concentration (µmol/L), and age is expressed in years; INR, international normalized ratio; SD, standard deviation.
*Neurodegenerative disease includes dementia and Parkinson’s disease. Conditions included in the Charlson Comorbidity Index include myocardial infarction, congestive cardiac failure, peripheral vascular disease, cerebrovascular disease, dementia, chronic obstructive pulmonary disease, connective tissue disease, peptic ulcer disease, liver disease (mild vs. moderate to severe), diabetes (with or without organ damage), hemiplegia, moderate to severe renal disease, any tumor (within last 5 years), lymphoma, leukemia, metastatic solid tumor and acquired immunodeficiency syndrome (AIDS). The simplified Pulmonary Embolism Severity Index incorporates age, history of malignancy, cardiac failure or chronic pulmonary disease, heart rate ≥110 beats per minute, systolic blood pressure <100 mmHg and arterial oxyhemoglobin <90% at admission.
†Laboratory parameters were retrieved in 771/773 (99.7%) for estimated GFR; serum hemoglobin in 769/773 (99.5%); INR on admission in 725/773 (93.8%); INR on discharge in 722/773 (93.4%).
‡p<0.05 compared to Group 1.
§p<0.05 compared to Group 2.
‖p<0.05 compared to Group 3.