title: A prospective evaluation of the glomerular filtration rate in older adults with frequent nighttime urination.
abstract: OBJECTIVE
  We assessed the association of renal function with frequent nighttime urination in older adults.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Atlanta Veterans Affairs Rehabilitation Research and Development Center, Decatur, Georgia.
authors.forename: Theodore M
authors.initials: TM
authors.lastname: Johnson
authors.forename: Jeff M
authors.initials: JM
authors.lastname: Sands
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Ouslander
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003404:Creatinine / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D013995:Time; D014554:Urination / Q000502:physiology*
chemical_list: D003404:Creatinine