Urinary uric acid levels and discoloration of diapers in healthy neonates

Abstract

Sirs, Uric acid, a weak organic acid with a pKa of 5.75, is the end product of dietary and endogenous purine metabolism [1]. The normal range of plasma urate values is dependent on the population and varies with sex, ethnic and anthropometric differences [2]. In diapers of newborn infants, deposits of pink or red uric acid crystals have long been observed, creating panic in the family because of confusing it with blood. The observation of pink or red uric acid crystals in diapers of some neonates and not in others has led us to investigate the factors that effect crystallization. The relationship between urinary uric acid concentration and color change in diapers has not been investigated. We designed a study to find out whether or not there is a correlation between urinary uric acid concentration and pink to red color changes in the diapers of neonates. Urinary uric acid concentrations and urine examinations were evaluated after the completion of 24 h of age in 100 physiologically stable newborn infants (Table 1). Infants born with perinatal complications, those having a urine pH of <5.5 or hematuria or pyuria were excluded. Caregivers and mothers were informed about the investigation, informed consent was given, and parents were asked to report any color changes in diapers to the pediatrician. Diapers were also examined by three residents in pediatrics at each visit (three times a day) for the presence of pink or red color until discharge. The observers did not know the results of the urine examination at the time. All of the infants were breastfed. Urine collections were obtained from each infant using an external collecting device (urine bag), which was applied after the completion of 24 h of life. Urine specimens were studied for uric acid and creatinine by sequential multiple autoanalyzer at 37 C, with standards supplied by the manufacturer (Autoanalyzer, P-Module, Hitachi). The accepted normal range in the booklet supplied by the manufacturer for urinary uric acid was 37–92 mg/dl. Urine samples were also analyzed for urine pH, density and examined microscopically for pyuria and hematuria automatically (UEF-100, USA). Statistical analyses were conducted using the SPSS version 10.0 for Windows. The chi-square test was used to examine the significance of uric acid concentrations below and above the cutoff level in color positive and color negative groups. The Mann-Whitney U test was used for comparison of the means and ratios between the groups. P values lower than 0.05 were considered significant. The mean and median urinary uric acid concentrations for the color positive group were 105.9€80.7 mg/dl and 101.50 mg/dl, and those of the color negative group were 74.4€70.4 mg/dl and 55.50 mg/dl (P=0.151). Pink or red color was seen in the diapers of 22 neonates. There were 11 newborns whose uric acid concentrations were above 92 mg/dl, the highest level of accepted uric acid concentration in urine, in the color positive group. In the color negative group, uric acid concentrations were below 92 mg/dl in 26 neonates and above 92 mg/dl in 52 (P=0.153). For male infants, we also determined no significant difference (P=0.09) (Table 1). The mean concentration of urinary uric acid in infants born by normal spontaneous vaginal delivery was 85.1€67.0 mg/dl and of neonates born by cesarean section, 87.0€77.0 mg/dl (P=0.928). Urine density ranged between 1,001 and 1,025 (median=1,008.5, moderate=1,010) and pH between 5.5 and 8.0 (median=6.0, moderate=6.0). Microscopic examinations of the infants included in the study were all normal. No correlation was found between color positive and negative groups and urine density or pH. In neonates high urinary uric acid excretion has been shown by various researchers [3, 4, 5]. Since we know from the report of Monkus et al. [5] that the peak uric acid S. K peli · M. Yurdak k · G. Kilinc · E. Bilgetekin Department of Neonatology, Hacettepe University Ihsan Dogramaci Children’s Hospital, Ankara, Turkey