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 blood 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 specimens were obtained by suprapubic bladder aspiration and microscopically analyzed by the standard urinalysis (UA) and by hemocytometer WBC counts simultaneously, and quantitative urine cultures were performed. Receiver-operating characteristic (ROC) curves were constructed for each method of UA. The 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 1,000 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 bacterial colony count > or = 100,000 colony-forming units/ml, whereas the remaining had between 1,000 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 hemocytometer WBC counts, the presence of < or =10 WBC/microl appeared 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 power 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, specificity and likelihood ratio of hemocytometer WBC counts were also greater than that of standard UA (88.7, 89.6 and 8.08% vs. 84.3, 88.1 and 5.44%).

CONCLUSION: Hemocytometer WBC counts provide more valid and precise prediction of UTI in febrile infants than standard UA. The presence of > or =10 WBC/microl in suprapubic aspiration specimens is the optimum cutoff value for identifying febrile infants for whom urine culture is warranted.