Diagnosis of urinary tract infection by urine microscopy using a disposable counting chamber

Routine urinalysis is performed as a screening test for urinary tract infection (UTI), but is not very reliable. We assessed the usefulness of microscopic examination of unspun urine using a disposable slide with counting chambers for the diagnosis of UTI caused by a variety of species of bacilli. One hundred and seventy-two urine samples were obtained from 113 subjects (60 male and 53 female), including 84 inpatients, aged 20-96 years. The urine samples were examined for bacteriuria and pyuria using a counting chamber, and the reliability of this method in predicting significant bacteriuria defined by routine urine culture and Gram stain of urine smears was analyzed. Significant bacteriuria was diagnosed in 68 urine samples, including 34 from indwelling catheters, from 52 patients mostly having underlying diseases. Only 12 of the positive urine samples contained E. coli, with a variety of other bacilli including cocci found in the rest. The counting chamber method detected bacteriuria in 64 of these 68 positive samples (sensitivity = 94%). Specificity was 88%. While the sensitivity and specificity of pyuria (WBC > 10 microliters-1) were 79 and 71%, respectively, both sensitivity and negative predictive value were as high as 97% when bacteriuria or pyuria was present. We demonstrated that urine microscopy on a disposable counting chamber is a simple, sensitive and time- and cost-saving method for the diagnosis of UTI caused by a variety of bacterial species including cocci.