Evaluation of two commercial microtiter cytotoxin assays for the detection of Clostridium difficile toxin B in stool specimens

Two commercial microtiter cytotoxin assays using a fibroblast cell line (Bartels, Baxter Diagnostics, Inc., Deerfield, IL) and an epithelial cell line (Cytotoxi Test, Advanced Clinical Diagnostics, Toledo, OH) were evaluated for their ability to detect Clostridium difficile toxin B in stool specimens. After 48 hours, the assays had comparable sensitivity (90 versus 92%) and specificity (99 versus 98%). Although not statistically significant, the Bartels assay detected more toxin-positive specimens at 24 hours (84 versus 72%, P = 0.089, Fisher's Exact Test) and the Cytotoxi assay had fewer nonspecific reactions requiring repeat testing (2.2 versus 1.1%, P = 0.186, Fisher's Exact Test). Both cytotoxin assays had comparable analytic performance.