A laboratory result indicating the presence of Clostridioides difficile antigen but the absence of detectable toxin signifies that the bacteria are present in the patient’s stool sample, but are not, at the time of testing, producing the toxins that typically cause the symptoms of C. difficile infection (CDI). The antigen test detects a common C. difficile enzyme, glutamate dehydrogenase (GDH), which is produced by both toxigenic and non-toxigenic strains. Therefore, a positive antigen result suggests the presence of the bacteria. However, the absence of toxin, detected via toxin A/B assays, implies that the strain present may be non-toxigenic or is not currently producing toxins in sufficient quantity to be detected by the test. The absence of toxin suggests that symptoms are likely due to another cause.
This finding is important in the diagnosis and management of CDI. While the presence of the bacteria may raise suspicion, the lack of toxin production often suggests that the patient’s diarrheal symptoms are attributable to a different etiology. Historical context reveals that relying solely on antigen testing can lead to overdiagnosis, as asymptomatic carriage of C. difficile is common, particularly in hospitalized patients. Therefore, clinical guidelines emphasize the importance of toxin testing to confirm active infection before initiating treatment. This approach prevents unnecessary antibiotic use, which can contribute to antibiotic resistance and further disrupt the gut microbiome.
