Diagnosis of Clostridium Difficile: A Wrong Algorithm and an Improvement in Immunoassays

We compared the 2-step and 3-step algorithms for diagnosis of Clostridium difficile infection (CDI) in clinical cases between October and December 2023. We observed in 3-step algorithm 22 false positives (FP) among the 62 positives (35%), compared to 40 positives without FP in 2-step algorithm. 30 All FP are positive for glutamate dehydrogenase (GDH) and Toxin A and/or B immunochromatography (IC), and negative for toxigenic C.difficile PCR. When processing the samples with a solution of leukocidins and Methicillin Resistant Staphylococcus aureus (MRSA) the FP to GDH is negative, as well as FP from different immunoassays. The cause of FP is an interspecies cross-reaction between human leukocytes and mouse immunoglobulins, a methoddependent error (immunoassay) that increases the 35 probabilities of FP in the 3-step algorithm. Modified algorithms and sample processing with MRSA and leukocidins allow equivalent results to the 2-step algorithm, with a reduction in the total number of molecular tests required (47-61%).