The authors determined the value of performing urine microscopy on biochemically negative urine specimens in a pediatric population. Four reactions of the Chemstrip-9TM (Biodynamics, Inc., Indianapolis, IN) were used as biochemical indicators, namely, protein, occult blood, leukocyte esterase, and nitrite. Out of 1,016 urine specimens thus studied, 310 were true positive. Eleven specimens reacted biochemically in the absence of significant microscopic findings (false positive), 668 specimens were negative by the Chemstrip-9 and were either negative microscopically or had less than five white blood cells (WBCs) per high power field (HPF) and were considered true negatives. Twenty-seven specimens had negative biochemical indicators, in spite of positive microscopy; of these specimens, only seven had more than ten WBCs per HPF, 17 had five to ten WBCs per HPF, and three had five to ten red blood cells per HPF. The sensitivity of the four parameters for predicting significant microscopy of urinary sediment is 91% and the specificity is 98%. The predictive value of a negative result is 96.1%, and that of a positive result is 96.5%. The authors therefore conclude that urine microscopy is unnecessary in biochemically negative urine specimens from pediatric patients who are asymptomatic for urinary tract disease.
Results with two ultramicro methods for plasma uric acid analysis with uricase are described: a crystal violet (gentian violet) method, modified from an automated procedure by Gochman and Schmitz [Clin. Chem. 17, 1154 (1971)] and adapted to manual analysis, and a polarographic oxygen-sensing system (Beckman Instruments, Inc.). The coefficient of variation (CV) for the crystal violet method varied between 2.1 and 5.7% for an 11-month period. Within-run precision (CV) of the polarographic method was 3.3%; day-to-day CV varied between 3.4 and 9.4%. Percentage recovery for the crystal violet method ranged between 97 and 106%, and for the polarographic method between 92 and 100%. Results of the two methods correlate well, but 5-15% lower values are obtained by the crystal violet method than by the polarographic method. Bilirubin, hemolysis, or usual plasma concentrations of ascorbic acid do not interfere significantly with either method. Advantages and disadvantages of both methods are discussed. The polarographic method requires more uricase, but is the better of the two methods.
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