Comparison of hemocytometer leukocyte counts and standard urinalyses for predicting urinary tract infections in febrile infants

Objectives. To compare the accuracy of standard and hemocytometer white blo od cell (WBC) counts and urinalyses for predicting urinary tract infection (UTI) in febrile infants. Methods. Enrolled were 230 febrile infants <12 months of age. All urine spe cimens were obtained by suprapubic bladder aspiration and mi croscopically analyzed by the standard urinalysis (UA) and by hemocytometer WBC counts si multaneously, and quantitative urine cultures were performed. Receiver-oper ating characteristic (ROC) curves were constructed for each method of UA, T he optimal cutoff point of the UA test in predicting UTI was determined by ROC analysis. Results. There were 37 positive urine cultures of at least 1000 CFU/ml, Of these 37 patients, 9 females and 28 males, 1 had a positive blood culture ( Escherichia coli), Thirty (81%) of the positive urine cultures had a bacter ial colony count greater than or equal to 100 000 colony-forming units/ml, whereas the remaining had between 1000 and 50 000 colony-forming units/ml. The area under the ROC curve for standard UA was 0.790 +/- 0.053, compared with 0.900 +/- 0.039 for hemocytometer WBC counts (P < 0.05), For hemocytom eter WBC counts, the presence of greater than or equal to 10 WBC/mu l appea red to be the most useful cutoff point, yielding a high sensitivity (83.8%) and specificity (89.6%). Standard UA, with a cutoff point of 5 WBC/high po wer field, had a lower sensitivity (64.9%) and similar specificity (88.1%). The hemocytometer WBC counts showed significantly greater sensitivity and positive predictive value (83.8 and 60.8%, respectively) than the standard urinalysis (64.9 and 51.1%, respectively) (P < 0.05), The accuracy, specifi city and likelihood ratio of hemocytometer WBC counts were also greater tha n that of standard UA (88.7, 89.6 and 8.08% us. 84.3, 88.1 and 5.44%), Conclusion. Hemocytometer WBC counts provide more valid and precise predict ion of UTI in febrile infants than standard UA, The presence of greater tha n or equal to 10 WBC/mu l in suprapubic aspiration specimens is the optimum cutoff value for identifying febrile infants for whom urine culture is war ranted.