Analysis of the disagreement between automated bioluminescence-based and culture methods for detecting significant...

A fully automated method for detecting significant bacteriuria is described which uses firefly luciferin and luciferase to detect bacterial ATP in urine. The automated method was calibrated and evaluated, using 308 urine specimens, against two reference culture methods. We obtained a specificity of 0.79 and sensitivity of 0.75 using a quantitative pour plate reference test and a specificity of 0.79 and a sensitivity of 0.90 using a semiquantitative standard loop reference test. The majority of specimens negative by the automated test but positive by the pour plate reference test were specimens which grew several bacterial species. We suggest that such disagreement was most likely for urine containing around 10(5) colony-forming units per ml (the culture threshold of positivity) and that these specimens were ones contaminated by urethral or vaginal flora. We propose standard procedures for calibrating and evaluating rapid or automated methods for the detection of significant bacteriuria and have analyzed our results using these procedures. We recommend that identical analyses should be reported for other evaluations of bacteriuria detection methods.