Serum and Urine Osmolality as Predictors of Adequate Diuresis in Acute Decompensated Heart Failure: A Prospective Cohort Study

Background: Determination of adequacy of decongestion remains a significant challenge in the management of acute heart failure (AHF). Methods: This is a prospective single center cohort study of patients (>18 years old) admitted for AHF on intravenous diuretics, with BNP >100 pg/mL or echocardiographic findings of reduced ejection fraction or diastolic dysfunction, and at least 1 clinical sign of volume overload. Patients with eGFR ≤45 mL/min or on dialysis, and with exposure to contrast dye or nephrotoxins were excluded. Serum and spot urine osmolality were obtained in the early morning simultaneously daily for 5 days or until discharge. Receiver operating characteristic curves were used to analyze the optimal cutoffs for the osmolality values in the prediction of heart failure (HF) readmissions Results: Of the total 100 patients, 62% were male and 59% were Black American. The mean age was 64.41 ± 12.53 and 34% had preserved ejection fraction. Patients with 30-day readmission had higher serum osmolality (mOsm/kg) on admission (305 [299–310] vs. 298 [294–303]; p = 0.044) and had higher drop in serum osmolality between admission and discharge (−7.5 [−9.0, −1.25] vs. −1.0 [−4.0, 4.0]; p = 0.044). Serum osmolality on admission of >299 mOsm/kg (sensitivity: 83%, specificity: 61%) and drop in serum osmolality between admission and discharge of >2 mOsm/kg (sensitivity: 83%, specificity: 65%) was associated with 30-day HF readmissions. No patients discharged with urine osmolality more than 500 mOsm/kg had 30-day readmissions, but this was not statistically significant, p = 0.334. Conclusion: Measurement of serum osmolality and urine osmolality may have some utility in AHF, but interpretation should consider baseline values and dynamic changes to account for individual differences in sodium and water handling.