Clostridium difficile infection laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Yazan Daaboul, M.D.
Overview
Testing is generally not necessarily for patients with formed stools (no diarrhea). Among patients with diarrhea,C. difficile infection is diagnosed either by enzyme immunoassay (ELISA) for toxins A and/or B in stools or by DNA-based tests (PCR) that detect bacterial toxin genes in stools. Although both ELISA and DNA-based tests may be performed sequentially, only one positive test is sufficient to diagnose C. difficile infection. Both ELISA and DNA-based tests also have a high negative predictive value > 95% among average-risk patients, and generally negative results warrants the search for alternative diagnoses. The advantage of DNA-based tests over ELISA is that it may detect the presence of BI/NAP1/027 strain, which alters the management plan. However, DNA-based tests may also detect clinically irrelevant findings that may delay the diagnosis. Stool culture requires anaerobic culture and may not be available. Although not diagnostic, additional blood testing may be necessary to monitor for possible development of complications or the success/failure of antimicrobial therapy.
Laboratory Findings
Testing is generally not necessarily for patients with formed stools (no diarrhea). Among patients with diarrhea, C. difficile infection is diagnosed either by enzyme immunoassay (ELISA) for toxins A and/or B in stools or by DNA-based tests that detect bacterial toxin genes in stools. Although not diagnostic, additional blood testing may be necessary to monitor for possible development of complications or the success/failure of antimicrobial therapy.
Blood Work-Up
Complete blood count with differential
- Leukocytosis with left shift
- Leucopenia is occasionally reported
Electrolytes
Inflammatory markers
Inflammatory markers, such as CRP or ESR may be helpful for follow-up of patients with C. difficile infection or a non-specific means to monitor the success of antimicrobial therapy.
Coagulation profile
- Coagulation profile, such as PTT, PT, and INR should be ready because surgery may be required among patients with complicated disease.
Albumin
Stool Work-Up
Stool analysis
- Leukocytosis
- Blood in stools
Enzyme-linked immunoabsorbant assay (ELISA) for toxin
- Assessment of the A and B toxins by enzyme-linked immunoabsorbant assay (ELISA) for toxin A or B (or both) is generally sensitive and specific:
- Sensitivity 63-99%
- Specificity 93-100%
- Negative predictive value > 95% for patients with average risk (generally if ELISA negative, search for alternative diagnoses warranted)
- Following successful antimicrobial therapy, patients may remain positive for many weeks/months. No additional treatment recommended.
- ELISA and DNA-based tests (below) may be used sequentially, but one positive result is sufficient for diagnosis.
DNA-based tests
- Higher sensitivity and specificity than ELISA
- Negative predictive value > 95% for patients with average risk (generally if DNA-based tests negative, search for alternative diagnoses warranted)
- Identify microbial toxin genes and toxicogenic strains in unformed stools
- Detects presence of BI/NAP1/027 strain
- May detect clinically irrelevant findings.
- Following successful antimicrobial therapy, patients may remain positive for many weeks/months. No additional treatment recommended.
- DNA-based tests and ELISA (above) may be used sequentially, but one positive result is sufficient for diagnosis.
Stool culture
- Anaerobic culture needed.
- Not widely available.