Clostridium difficile TOX A/B II TEST Evaluation

Abstract

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 0.35ng/mL and Uniquick at concentrations of 0.7ng/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.