0823 Age-Related Changes in Nocturnal Urine Composition

Abstract

Abstract Introduction In humans sleeping nocturnally, nocturnal polyuria (NP) refers to high rate of overnight urine production. NP is a heterogeneous condition that may reflect both free water and/or sodium diuresis, but the influence of age on differential fluid handling remains poorly understood. This study examined diuresis rate, sodium clearance, and free water clearance (FWC) by age, time of day (nighttime vs. daytime) and NP status (positive/negative) in subjects under entrained conditions sleeping nocturnally. Methods Convenience samples (age range 18-91; 82 men, 148 women) recruited from a urology ambulatory care unit (n=135) or continence clinic (n=95) collected 8 urine samples at 3-hour intervals over a single 24-hr period. Three separate mixed linear models were constructed for diuresis rate, sodium clearance, and FWC using four predictors: NP status (present [>90mL/h] vs. absent), time of day (night = 0100, 0400, 0700), age (as a continuous measure), and study source. Results Subjects with NP experienced both higher nighttime vs. daytime diuresis rate (1.89 vs. 1.44 mL/min, p<0.001), sodium clearance (0.91 vs. 0.74 mL/min, p<0.001), and FWC (-0.38 vs. -0.71 mL/min, p<0.001), whereas subjects without NP demonstrated lower nighttime vs. daytime diuresis rate (0.94 vs. 1.06, p=0.004) and no difference in sodium clearance (0.59 vs. 0.64, p=0.120) or FWC (-0.80 vs. -0.86, p=0.268). Regardless of NP status, FWC increased with age (p=0.039), and older age (>70) was accompanied by an increase in the ratio of nighttime/daytime diuresis rate and both nighttime and daytime sodium clearance. Conclusion Irrespective of NP, older adults experience proportionally greater nocturnal sodium clearance, as well as a complex surge in both daytime and nighttime FWC. The data imply that both nocturnal sodium clearance and FWC may reflect the relevant substrate underlying excess nocturnal urine production in elderly persons. Support N/A