Do vesical and voided urine have identical compositions?

Abstract

Objective: In view of the concept that the urothelium is a functioning epithelium, we investigated the hypothesis that the composition of urine is modified as it passes through the urethra from the urinary bladder to the exterior.

Material and methods: The study was performed in 22 healthy volunteers (13 males, 9 females; mean age 44.6+/-6.2 years). Vesical and voided urine were collected separately; pH was determined using a pH electrode, osmolality by means of micro-osmometry and electrolytes (Na, K) using flame photometry.

Results: Voided urine showed significant increases in pH, osmolality and Na and K concentrations compared to urine contained in the bladder (p < 0.05 for each). Gender and age differences were not significant.

Conclusions: Vesical urine undergoes changes in some of its components during its passage through the urethra. These findings presumably indicate that the urethral urothelium is a functioning epithelium and also that voided and vesical urine are not identical. The study raises the question to what extent is the analysis of voided urine representative of that of vesical urine?