A prospective evaluation of the glomerular filtration rate in older adults with frequent nighttime urination.

Abstract

We assessed the association of renal function with frequent nighttime urination in older adults. We recruited a convenience sample of 48 adults 65 years old and older, and admitted them to a general clinical research center. Of the 48 participants 45 completed a 7-day voiding record, ate a research diet for 4 days and finished a 3-day stay with 3 glomerular filtration rate measurements, including an estimation of serum creatinine using the Cockcroft-Gault formula, a calculation using 24-hour urine volume and a determination by 131iodine iothalamate clearance. Subjects with frequent nighttime voiding, defined as a mean of 2 or more voiding episodes from 11 p.m. to 7 a.m., had slightly lower but statistically similar glomerular filtration rate measurements than those with a mean of less than 2 nighttime voids. The glomerular filtration rate did not correlate with the number of nighttime voids (Pearson correlation coefficient -0.006, p = 0.971). Mean 24-hour urine output was similar in the 2 groups and the correlation of the number of nighttime voids with 24-hour urine output was insignificant (Pearson correlation coefficient -0.06, p = 0.683). A greater number of nighttime voids was associated with producing more urine at night and smaller mean voided volume. As determined by a gold standard glomerular filtration rate measurement, renal function was not associated with the number of nighttime voids in our study population. Total 24-hour urine output was also not associated with the number of nighttime voids. Our findings confirmed the positive association of a greater number of nighttime voids with greater nighttime urine production and lower bladder voided volume.