<i>Clostridium difficile </i>TOX A/B II TEST Evaluation

We compared the performance of two commercial toxin detection kits, C. difficile toxin A/B (C. difficile TOX A/B II test; TOX A/B II) and C. difficile toxin A (Uniquick), for (i) detection using highly purified toxin A solution; (ii) cross-reactivity using culture supernatants of toxin A-positive and B-positive C. difficile, toxin A-negative and B-positive C. difficile, and toxin A-negative and B-negative C. difficile strains and other bacteria; and (iii) sensitivity and specificity using clinical specimens. Results indicated that TOX A/B II detected toxin A at concentrations of 0.35 ng/mL and Uniquick at concentrations of 0.7 ng/mL. Uniquick performance was specific for detecting toxin A alone, while TOX A/B II detected toxin A/B specifically. Kit performance was then evaluated using 99 fecal specimens--43 specimens from patients with toxin B-positive C. difficile and 56 from those without. Sensitivity of TOX A/B II vs Uniquick was 95.3% vs 76.7%, specificity 98.2% vs 98.2%, positive predictive 97.6% vs 97.1%, and negative predictive value 96.5% vs 84.6%. Findings thus indicate that TOX A/B II is a more suitable diagnostic aid for CDAD than Uniquick because it correlates well with toxin B-positive C. difficile culture results. Stool culture for C. difficile is also required, however.