Call option and put option

False-negative examinations are an important concern for clinicians. Some EIA examinations can detect both toxin A and B; others test only for toxin A and a common clostridial antigen that acts as surrogate marker for the presence of clostridia. Thus, confirmation for toxin B via examinations such as toxin B assay or polymerase chain reaction is necessary when the EIA for toxin A is negative but the common clostridial antigen is positive.

In short, clinical judgment is still very important in diagnosis.