Performance of two rapid, single-use immunoassays for the detection of Clostridium difficile toxin A

Two rapid, single-use immunoassays for C. difficile toxin A, the Clearview C. DIFF A (Wampole Laboratories, Cranbury, N.J.) and the ImmunoCard Toxin A assays (Meridian Diagnostics Inc., Cincinnati, Ohio) were compared to the cytotoxin assay for their ability to detect C. difficile toxin in fecal specimens. A total of 537 specimens were tested and 47 (8.8%) were positive by the cytotoxin assay. The sensitivity, specificity, positive predictive value, and negative predictive value of the toxin A assays were as follows: 70.2% (95% CI, 57.1 to 83.3), 98.8% (95% CI, 97.8 to 99.8), 84.6% (95% CI, 73.3 to 95.9), and 97.2% (95% CI, 95.7 to 98.6) respectively for the Clearview assay; and 74.5% (95% CI, 62.0 to 86.9), 99.0% (95% CI, 98.1 to 99.9), 87.5% (95% CI, 77.3 to 97.8), and 97.6% (95% CI, 96.2 to 98.9) respectively for the ImmunoCard assay. Both toxin A assays are less sensitive than the cytotoxin assay, however, these assays offer a rapid and easy-to-perform test that may be used in conjunction with the cytotoxin assay for laboratory confirmation of C. difficile-associated disease.