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BACKGROUND Hyponatremia is the most common electrolyte abnormality observed in clinical practice. Among patients with acute coronary syndrome (ACS), serum sodium levels are inversely associated with mortality risk. We assessed associations of serum sodium level with ACS and mortality in patients with chest pain. METHODS This retrospective cohort study used clinical data from a large, academic hospital. All adults admitted with chest pain and without hypernatremia and discharged after ACS rule-out from January 2010 through June 2016 were included. The primary endpoint was the composite of 30-day ACS and mortality. Secondary endpoints were a hospital admission due to ACS and mortality in the first year following discharge. RESULTS Included were 12 315 patients (mean age 58.2 ± 13 years, 60% male). Patients were classified according to the serum sodium (Na) level: hyponatremia, defined as less than 135 mEq/L (n = 289, 2.3%); 140 > Na ≥ 135 mEq/L (n = 8066, 65.5%), and 145 > Na ≥ 140 mEq/L (n = 3960, 32.2%). Patients with serum sodium more than 145 mEq/L were excluded. Among patients with hyponatremia, low-normal, and high-normal levels, rates of the composite outcome of unadjusted 30-day all-cause mortality and ACS admission were 4.5, 1.0, and 0.7%, respectively (P < 0.001). Unadjusted one-year ACS rates were 3.8, 1.5, and 1.4%, respectively (P < 0.01). CONCLUSION Hyponatremia is associated with higher mortality and ACS risk among patients with chest pain who were discharged from internal medicine wards following ACS-rule-out. Sodium level may be included in the risk stratification of patients with chest pain.

Currently, there are no clinical scores for risk stratification of low-risk patients with chest pain. We aimed to examine the association between mean platelet volume (MPV) and risk for adverse clinical outcomes in patients with chest pain discharged from internal medicine wards following acute coronary syndrome (ACS) rule-out.Included were patients who were admitted to internal medicine wards and were discharged following an ACS-rule-out during 2010-2016. The primary endpoint was the composite of all-cause mortality and hospital admission due to ACS at 30-days following hospital discharge.Included in the study were12 440 patients who were divided into three groups according to MPV. The composite endpoint of 30-day all-cause mortality and hospital admission for ACS occurred more frequently among patients with high MPV. Each one-point increase in MPV was associated with an 18% increase in the risk for the composite endpoint (P = 0.02). Considering patients with MPV less than 7.8 fl as the reference group yielded adjusted hazard ratios for the composite endpoint that was significantly higher in patients in the high MPV tertile (8.8 fl) (hazard ratio 1.6; 95% confidence interval = 1.1-2.5; P = 0.04). Each one-point increase in MPV was associated with an 11% increase in the risk for 1-year all-cause mortality (P = 0.01) and a 10% increase in the risk for 1-year ACS (P = 0.04).We found an independent association between high MPV and the risk of death and ACS among patients with chest pain who were discharged from internal medicine wards following an ACS-rule-out. MPV may be combined in the risk stratification of patients with chest pain.