Clostridioides difficile and C. difficile Toxin Testing

You do not need to do anything special before providing a sample. 

You will need to collect a fresh stool sample in a sterile container. Your healthcare team will give you one. Do not let the sample touch water or urine, as this can affect the result. 

The sample must reach the laboratory as quickly as possible. C. difficile toxins can break down within one to two hours at room temperature. A delayed sample can give a false negative result. If there will be a delay, store the container in a designated refrigerator.

What the test measures 

C. difficile is a bacterium that lives in the gut of many healthy people without causing harm. Problems start when something upsets the balance of bacteria in your gut. Antibiotics are the most common cause. They can wipe out the helpful bacteria that normally keep C. difficile in check. 

When C. difficile is allowed to overgrow, about 75% of strains produce two toxins: toxin A and toxin B. These toxins damage the lining of the gut and cause diarrhoea and inflammation. This is called C. difficile infection (CDI). 

Laboratories use a combination of tests to detect CDI. No single test is perfect on its own. The most common approaches include: 

• Toxin enzyme immunoassay (EIA): directly detects toxins A and B in your stool. Results are available within hours but can miss up to 30% of cases. 
• Glutamate dehydrogenase (GDH) EIA: detects a protein made by C. difficile. It cannot confirm CDI on its own, but a negative result can help rule it out. 
• Molecular test (PCR): detects the genes that produce the toxins. It is fast and very sensitive but cannot distinguish between infection and simple carriage (having the bacterium without it causing disease). 
• Culture: grows C. difficile from your stool sample. Takes two to three days. Most often recommended for use during outbreaks. 

UK Department of Health guidance recommends a two-step approach: first a molecular test or GDH EIA, then a toxin EIA test.

If your result is positive 

A positive result means C. difficile toxins have been found in your stool. It is likely that C. difficile is causing your diarrhoea. 

Your doctor will review any antibiotics you are taking. They may switch you to a different one or stop it altogether. They will also prescribe a specific antibiotic to treat the C. difficile infection, such as vancomycin, or fidaxomicin. 

You will also receive supportive care to prevent dehydration. Your doctor will work with you to monitor your recovery and check for any complications. 

If your result is negative 

A negative result suggests that C. difficile toxins were not detected. This may mean your diarrhoea has another cause, such as a viral infection, another bacterial infection, a reaction to medication, or a bowel condition such as irritable bowel syndrome (IBS). 

However, a negative result does not always mean CDI is completely ruled out. The toxin can break down quickly, especially if the sample was not processed promptly. If your diarrhoea continues, your doctor may arrange for another sample to be tested. 

Your doctor will explain what the result means for you and whether any further investigation is needed. 

If you test positive, treatment will usually begin straight away. Most people improve once the right antibiotic is prescribed and any triggering antibiotic is stopped or changed. 

About 20% of people have a recurrence, where symptoms and toxins return after initial treatment. This usually happens because the normal gut bacteria have not fully re-established themselves. If your symptoms return, let your doctor know. You may need further testing and a different course of treatment. 

If your result is negative but diarrhoea continues, your doctor will look for other causes and may request additional tests.

Several factors can affect the accuracy of C. difficile testing: 

• Sample freshness: C. difficile toxins break down quickly. A sample that is not processed within one to two hours may give a false negative result. 
• Sample contamination: contact with urine or water can affect the test. 
• Formed stool: the sample must be unformed (liquid or soft) and fill at least a quarter of the container. Formed stools are not suitable for testing. 
• Visible blood in the stool: this can occasionally cause a false positive result. 
• Anti-diarrhoea medicines: medicines such as loperamide can slow the passage of stool through your gut. This increases the time your gut lining is exposed to the toxin and may make your infection worse. Avoid them unless your doctor says otherwise. 

Your doctor may arrange additional tests depending on your symptoms and how unwell you are. These might include: 

• Stool culture: to look for other bacteria that could be causing your diarrhoea, such as Salmonella or Campylobacter. 
• Blood tests: to check your white blood cell count and look for signs of infection or inflammation. 
• Endoscopy: a specialist (gastroenterologist) can look directly at the lining of your colon using a flexible camera. This can detect characteristic patches of inflammation called pseudomembranous lesions. 

Your doctor will discuss which tests are right for you. 

C. difficile infection (CDI) is one of the most common causes of antibiotic-associated diarrhoea in hospitals. Symptoms range from mild diarrhoea to severe inflammation of the colon.