What is a Clostridium difficile Toxins A & B test?
This test detects toxins A and B produced by Clostridioides difficile (C. difficile) in a stool sample.
C. difficile is a type of bacterium that can live in the intestine without causing illness in some people. However, when the normal balance of intestinal bacteria is disrupted—often after treatment with antibiotics—C. difficile can multiply and produce toxins.
The two major toxins are:
Toxin A (enterotoxin)
Toxin B (cytotoxin)
These toxins can damage the lining of the colon and cause inflammation, leading to C. difficile infection (CDI).
A toxin A & B test can help determine whether diarrhea and other intestinal symptoms may be caused by toxin-producing C. difficile.
Other names: C. difficile toxin A/B, C. difficile toxins, C. difficile toxin assay, Clostridioides difficile toxins A and B, C. diff toxin test.
What is it used for?
A Clostridium difficile Toxins A & B test may be used to help:
Diagnose C. difficile infection
The test can help determine whether a patient with symptoms of diarrhea may have an active infection caused by toxin-producing C. difficile.
Investigate antibiotic-associated diarrhea
Antibiotic treatment can disrupt the normal bacteria in the intestine and allow C. difficile to grow.
Testing may be considered when significant diarrhea develops during or after antibiotic treatment.
Evaluate symptoms of colitis
C. difficile infection can cause inflammation of the colon (colitis), which may result in:
Frequent watery diarrhea
Abdominal pain or cramping
Fever
Nausea
Loss of appetite
Abdominal tenderness
In more severe cases, complications can occur.
Help guide clinical management
A positive toxin result, together with the patient's symptoms and other laboratory findings, can support the diagnosis and help healthcare providers determine appropriate treatment.
Why do I need a Clostridium difficile Toxins A & B test?
You may need this test if you have unexplained watery or frequent diarrhea, particularly if you:
Recently used antibiotics
Were recently hospitalized or stayed in a healthcare facility
Have a history of C. difficile infection
Develop diarrhea after recent healthcare exposure
Have abdominal pain or cramping together with significant diarrhea
Have other symptoms suggesting inflammation of the colon
Your healthcare provider may also order additional tests depending on your symptoms and clinical condition.
What happens during a Clostridium difficile Toxins A & B test?
The test requires a stool sample.
You will be given a clean container for collecting the specimen.
To collect the sample:
Pass the stool into a clean, dry container or collection device.
Avoid mixing the stool with urine, toilet water, or toilet paper.
Place the required amount of stool into the specimen container.
Close the container securely.
Return the specimen to the laboratory as instructed.
The laboratory may provide specific collection and storage instructions.
Formed or solid stool is generally not appropriate for testing for active C. difficile diarrhea, because asymptomatic colonization can occur and testing is intended primarily for patients with clinically significant diarrhea.
Will I need to do anything to prepare for the test?
Usually, no special preparation or fasting is required.
Tell your healthcare provider if you have recently taken:
Antibiotics
Antidiarrheal medications
Proton pump inhibitors or other medications that may affect your gastrointestinal condition
Do not stop any medication unless your healthcare provider tells you to do so.
Are there any risks to the test?
There are no direct risks associated with collecting a stool sample.
The main concern is obtaining an adequate and uncontaminated specimen for accurate testing.
What do the results mean?
The result is generally reported as Positive/Detected or Negative/Not detected, depending on the laboratory method.
The result must be interpreted together with the patient's symptoms and clinical history.
A positive result
A positive toxin A & B result means that C. difficile toxin(s) were detected in the stool sample.
In a patient with compatible symptoms, this supports a diagnosis of toxin-producing C. difficile infection.
A positive result may be associated with:
C. difficile-associated diarrhea
C. difficile colitis
Other forms of symptomatic C. difficile infection
Treatment should be determined by the healthcare provider based on the patient's clinical condition.
A negative result
A negative result means that C. difficile toxin A and B were not detected in the tested stool specimen.
A negative result makes toxin-mediated C. difficile infection less likely, but it does not always completely exclude infection.
The sensitivity of toxin immunoassays is lower than some molecular tests, so if clinical suspicion remains high, the healthcare provider may consider additional testing or a different diagnostic algorithm.
Important note about Clostridium difficile Toxins A & B results
Detection of C. difficile requires careful interpretation because colonization and infection are not the same thing.
Some people can carry C. difficile in their intestine without having symptoms. Therefore, testing is generally recommended for patients with clinically significant diarrhea, rather than routinely testing asymptomatic individuals.
Many laboratories use a diagnostic algorithm involving glutamate dehydrogenase (GDH), toxin A/B testing, and/or nucleic acid amplification testing (NAAT/PCR).
A PCR/NAAT-positive result does not necessarily mean that active toxin-mediated disease is present, because molecular tests detect the organism's toxin genes rather than the toxin itself. Conversely, toxin assays may be less sensitive.
Therefore, the laboratory result should always be interpreted together with the patient's symptoms, specimen quality, and the testing algorithm used by the laboratory.
Repeat testing during the same episode of diarrhea is generally not recommended as a test of cure, because laboratory results may remain positive after clinical recovery.
Prefer to talk to someone first? Contact us to book.
