SUMMARY A procedure for estimating 24 hour urine output in infants using disposable nappies has been validated. In addition, it has been shown experimentally that the urinary concentrations, and hence 24 hour outputs of a range of constituents (sodium, potassium, nitrogen, creatinine, urea, amino acids, and deuterium oxide), may be measured accurately using samples of urine obtained from nappies. It is concluded that the urine collection procedure described has several major advantages over traditional urine bag methods, and has a wide application in clinical practice and research.Urine is the body fluid most available for clinical monitoring and research in infants. Concentrations and daily output rates of a wide range of natural constituents of urine are measured frequently in clinical practice, and in renal, metabolic, and nutritional studies. There has also been interest in using information on urinary concentrations of harmless substances administered orally, to quantify body composition and aspects of metabolism such as protein turnover.1 2 Usually, urine is collected from infants by means of a urine bag, which can be aspirated continually if 24 hour values are required. This procedure is far from ideal; it is difficult to use effectively on girls, frequent monitoring is required, and bag displacement is common, especially in the older mobile infants. In addition, repeated application of bags may cause discomfort and excoriation of the skin. A simple, alternative procedure would be to extract urine from the infants' nappies or from cotton wool balls placed inside the nappy. The effects, however, if any, of these procedures on the concentrations of urinary constituents have received little attention. Moreover, it has not been established whether samples collected in this way could be used to provide information on 24 hour output rates of urine, bearing in mind the inevitable loss of a proportion of samples due to mixing of urine with stools.In this study we describe a procedure for extracting urine from disposable nappies, and have assessed its effects on the concentrations of a number of urinary constituents. In addition we have investigated whether a nappy collection procedure can be used to measure accurately 24 hour urine output.
MethodsStudy 1: effects of a nappy extraction procedure on concentrations of urinary constituents. Urine enriched with 0-01% deuterium oxide (2H20-a stable isotope of water used in studies on growth and body composition) was added in varying amounts (5 to 45 ml) to disposable nappies (Pampers, Proctor and Gamble). Each nappy contained a cotton wool ball to facilitate subsequent extraction of a sample when the urine volume was small. The nappies were sealed in plastic bags and incubated at 34 to 36°C for 0-5 to 10 hours, to simulate a range of normal use. Two nappies were used for each experimental condition. Urine was extracted at the end of the incubation period by compressing the damp fibre from the nappy and wool ball inside a disposable syringe. The extracted urine and a sa...
