Evaluation of a rapid bacterial ATP assay for screening BAL samples from ICU patients submitted for quantitative bacterial cultures

Abstract

A novel application of a rapid diagnostic technique for the detection of significant bacterial pathogens (>/=10(4) cfu/mL) in bronchoalveolar lavage (BAL) samples from critically ill ventilated patients is described. This rapid diagnostic assay (UTIscreen, Coral Biotechnology, San Diego, CA) utilizes a luciferin-luciferase reaction to detect bacterial adenosine triphosphate (ATP) and is currently commercially available for screening bacteriuria in urine specimens. One hundred and twenty-eight BAL samples were examined microscopically with Gram's stain and tested in parallel using the bacterial ATP assay and standard quantitative culture. The sensitivity (Sn), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) for the detection of bacteria >/=10(4) cfu/ml in BAL specimens for the bacterial ATP assay was 87%, 59%, 39%, and 94%, and for the Gram's stain was 73%, 65%, 39%, and 89%, respectively. The diagnostic utility was improved by combining the results of Gram's stain/bacterial ATP assay results with Sn, Sp, PPV, and NPV of 97%, 38%, 32%, and 97% respectively. A combined negative rapid test consisting of Gram's stain/bacterial ATP assay rules out significant bacteria in BAL samples with a high degree of certainty. Future studies are needed to clinically validate these observations.