Inconsistent Detection of Bacteriuria With the Yellow IRIS Automated Urinalysis Workstation

Abstract

Several investigators have demonstrated that the Yellow IRIS™ automated urinalysis workstation improves both precision and sensitivity for detection of white blood cells, red blood cells, and other large particulate material in urine. However, detection of very small particles, such as bacteria, is much more difficult since it requires interpretation of the high-power, real-timeflow display. We have evaluated the ability of an experienced operator to visually detect clinically significant bacteriuria (greater than 105 colonies per milliliter of urine) with the Yellow IRIS. In oneseries of experiments, serial dilutions of Escherichia coli in pooled urine were submitted for both quantitative culture and analysis on the Yellow IRIS. With the culture results as the reference method, the sensitivity and specificity for 100 different prepared specimens were 78% and 76%, respectively. When 300 actual patient specimens were submitted for both quantitative urine culture and visual detection of bacteria on the Yellow IRIS, the sensitivity and specificity were 55% and 77%, respectively. We have also evaluated the ability of additional Yellow IRIS parameters, such as the nitrite test and detection of abnormal numbers of white blood cells, to enhance the prediction of significant bacteriuria. The inclusion of these parameters as markers of significant bacteriuria increased the sensitivity to 84% and decreased the specificity to 51%.