Rayon balls and disposable-diaper material selectively adsorb creatinine.

One method for the collection of urine samples from infants involves absorption of the urine on cotton balls placed in the diaper. Such samples are not timed and excretions are often expressed per mg of urinary creatinine. An assumption in this method is that the creatinine concentration is not changed by the absorption process. The concentration of creatinine in urine samples was measured before and after absorption of the urine by cotton balls, rayon balls, or diaper material over a range of wetness. For urine from both adults and infants, absorption on rayon balls and diaper material caused an important artifactual decrease in the concentration of creatinine. The effect was particularly striking in lightly wetted samples; the mean percent decrease was only 3 +/- 2% for cotton but was 9 +/- 5% for rayon (n = 10) and 13 +/- 4% for diaper material (n = 7). These data provide evidence that rayon balls and diaper material (and to a lesser extent cotton balls) selectively adsorb creatinine from human urine.