Add-On: Clostridium difficile EIA
The C. difficile enzyme immunoassay detects toxins A and B in unformed faeces, confirming toxigenic infection in patients with antibiotic-associated or nosocomial diarrhoea. It offers rapid, highly specific results but moderate sensitivity (70–85%), so a negative result in high clinical suspicion warrants repeat or molecular testing; only test unformed stool to avoid false-positive colonisation.
2
Biomarkers
Stool
Sample
2–4 business days
Turnaround
No
Fasting
What is the C. difficile EIA test?
The Clostridium difficile enzyme immunoassay detects toxins A and B in faeces, confirming toxigenic infection in patients with diarrhoea compatible with C. difficile colitis. It is ordered as an add-on to comprehensive stool panels or as a standalone investigation when antibiotic-associated or nosocomial diarrhoea is suspected and rapid differentiation from non-infectious causes is needed. EIA offers practical advantages — results within hours, high specificity, and the ability to demonstrate toxin rather than mere colonisation — but sensitivity is lower than nucleic acid amplification. Practitioners order it to guide isolation, antimicrobial therapy, and infection-control measures, recognising that a negative result in high clinical suspicion warrants repeat testing or escalation to a molecular assay.
What does the C. difficile EIA test measure?
Toxin A is a glucosylating enterotoxin that disrupts the actin cytoskeleton of colonocytes, leading to fluid secretion, mucosal inflammation, and colonic epithelial necrosis. Most toxigenic strains of Clostridioides (formerly Clostridium) difficile produce both toxin A and toxin B; rare strains produce toxin B alone.
Detection of toxin A in faeces confirms toxigenic C. difficile infection in a patient with compatible diarrhoea. Enzyme immunoassay is rapid and specific but less sensitive than nucleic acid amplification tests, so a negative result does not exclude infection if clinical suspicion is high.
Toxin B is the more potent cytotoxin produced by toxigenic C. difficile. Like toxin A, it inactivates Rho-family GTPases via glucosylation, causing cytoskeletal collapse, tight-junction disruption, and inflammatory cell infiltration. All pathogenic strains produce toxin B, making it an essential marker of infection.
Toxin B detection is the cornerstone of diagnosing C. difficile infection. This EIA offers a rapid faecal assay with high specificity; however, its moderate sensitivity means it is best used in combination with clinical criteria or followed by molecular testing in high-risk patients with a negative result.
Why is the C. difficile EIA test ordered?
- Investigation of acute diarrhoea (≥3 unformed stools in 24 hours) in patients with recent antibiotic exposure, particularly fluoroquinolones, clindamycin, cephalosporins, or penicillins
- Evaluation of nosocomial diarrhoea in hospitalised patients, especially those with prolonged admission or multiple antimicrobial courses
- Assessment of recurrent or persistent diarrhoea following C. difficile treatment, to distinguish relapse from alternative diagnoses
- Work-up of colitis with leucocytosis, fever, abdominal pain, or raised inflammatory markers in at-risk populations, including older adults and immunosuppressed patients
- Add-on testing to a comprehensive stool panel when antibiotic-associated diarrhoea is clinically suspected but the panel's organism screen is negative
- Rapid screening in outbreaks or high-prevalence settings where isolation decisions must be made before molecular confirmation is available
Sample collection and turnaround
Sample type
Stool
Fasting required
No
Collection method
At-home collection kit
Turnaround
2–4 business days
Collection notes
Patient collects an unformed (liquid or soft) stool specimen in the provided container, avoiding contamination with urine or toilet water. Refrigerate immediately and ship with the cold pack supplied in the kit; Genova Diagnostics provides pre-paid return shipping. Specimens must reach the laboratory within 72 hours of collection, or be frozen if a longer delay is unavoidable.
Specimen requirements
Minimum 5 g unformed faeces in a clean, sterile container. Do not test formed stool. Refrigerate at 2–8°C and transport on ice; toxins are labile at room temperature. If delay exceeds 72 hours, freeze at −20°C or below.
What can affect C. difficile EIA results?
Toxin EIA should only be performed on unformed faeces; formed specimens from asymptomatic carriers yield false-positive results because toxin detection does not distinguish infection from colonisation in the absence of diarrhoea.
C. difficile toxins are labile and degrade at room temperature; specimens must be refrigerated promptly and tested within 72 hours, or frozen if longer delays are unavoidable.
Antimicrobial therapy reduces toxin production and organism burden, so specimens collected after treatment initiation may yield false-negative results; ideally collect before starting therapy.
EIA has moderate sensitivity (70–85% depending on the assay), so a single negative result does not exclude infection; repeat testing or use of a more sensitive molecular method is appropriate if clinical suspicion remains high.
Contamination dilutes toxin concentration and may introduce inhibitors; collect faeces in a clean container and avoid contamination to preserve assay reliability.
What do C. difficile EIA results mean?
Elevated
Detection of toxin A and/or toxin B confirms toxigenic C. difficile infection in a patient with compatible diarrhoea. Treat according to guidelines (vancomycin or fidaxomicin for most cases; add bezlotoxumab or faecal microbiota transplant in recurrent infection) and implement contact precautions. Positive toxin in formed stool may reflect colonisation rather than infection and should not trigger treatment.
Normal
'Not detected' indicates either absence of toxigenic C. difficile or organism burden below the assay's detection limit. In patients with high clinical suspicion (recent antibiotics, nosocomial setting, leucocytosis, colitis on imaging), consider repeat testing after 24–48 hours or escalate to nucleic acid amplification. A negative result does not exclude infection.
Reduced
Not applicable — this is a qualitative assay reporting detected or not detected.
Note: EIA specificity is high (>95%), so a positive result is reliable; however, sensitivity is moderate (70–85%), and a negative result in high clinical suspicion warrants repeat or molecular testing. Only test unformed faeces — testing formed stool or asymptomatic patients leads to false-positive results from colonisation. Interpret in the clinical context, not in isolation, and do not use for test-of-cure, as toxin may persist after clinical resolution.
Frequently asked questions
EIA detects toxins A and B directly in faeces, indicating active toxin production, and offers high specificity but moderate sensitivity (70–85%). Nucleic acid amplification detects the genes encoding toxins, yielding higher sensitivity but potentially identifying colonised patients who are not actively infected. EIA is favoured when rapid, specific confirmation is needed; molecular tests are used when sensitivity is paramount or EIA is negative despite high suspicion.
How to access the C. difficile EIA test
The C. difficile EIA reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- McDonald LC, et al. Clinical practice guidelines for Clostridium difficile infection in adults and children: 2017 update by the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA). Clin Infect Dis. (2018)
- Crobach MJT, et al. European Society of Clinical Microbiology and Infectious Diseases: update of the diagnostic guidance document for Clostridium difficile infection. Clin Microbiol Infect. (2016)
- Polage CR, et al. Overdiagnosis of Clostridium difficile infection in the molecular test era. JAMA Intern Med. (2015)
- Planche TD, et al. Diagnosis of Clostridium difficile infection by toxin detection kits: a systematic review. Lancet Infect Dis. (2008)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.