C. diff Testing
Reviewed
Also called: C. difficile test, Clostridium difficile test, Glutamate dehydrogenase test (GDH), C. difficile toxin test, C. difficile culture, PCR for C. diff
C. diff testing checks a stool sample for signs of infection with Clostridioides difficile bacteria. The bacteria can release toxins that irritate the colon and cause diarrhea, abdominal pain, nausea, loss of appetite, and fever. Most infections occur while taking certain antibiotics or within weeks after finishing them. Testing is especially important if you have symptoms and are at high risk (e.g., recent antibiotic use, age 65 or older, recent hospital or nursing home stay, weakened immune system, or prior C. diff infection).
Specimen: stool (fresh loose or liquid sample)
Why this test may be ordered
- To find out if C. diff bacteria are causing diarrhea when no other cause is known
- To evaluate symptoms such as watery diarrhea three or more times a day, abdominal pain, nausea, loss of appetite, or fever
- To test people at high risk for C. diff infection (recent antibiotic use, age 65+, recent healthcare facility stay, weakened immune system, prior C. diff infection, or known exposure)
Preparation and collection
No special preparation is needed.
You will need to provide a fresh sample of loose or liquid stool. Your provider will give you a container or kit with instructions. In general: label the container with your name, collection date, and time; collect the sample using a clean, dry container or special paper/plastic wrap placed over the toilet; avoid mixing stool with urine, toilet paper, or toilet water; close the container tightly; wash your hands well with soap and water; return the container according to instructions. If you cannot return it right away, refrigerate the sample. For diaper samples, special instructions using plastic wrap inside a clean diaper will be provided. In some cases, a provider may use a swab to take a stool sample from the rectum.
There is no known risk to having C. diff testing.
Understanding results
There are several tests for C. diff that check for different signs of infection in your stool sample. Your provider may order a combination of two or more types of tests along with tests for other conditions that can cause diarrhea. Your provider will consider all your test results, your symptoms, and your medical history to figure out whether C. diff is causing your illness.
- Positive (abnormal): May mean that toxins from C. diff bacteria are causing your symptoms. You may be diagnosed with C. diff if your tests show that your sample contained C. diff toxin genes (genes from the types of C. diff that can cause illness) or C. diff toxins (toxins A and B). Limitation: A positive result on a GDH antigen test alone can show that C. diff is in your body, but it cannot tell if it is making you sick. Your provider will use additional tests to make an accurate diagnosis. Next step: If you are diagnosed with a C. diff infection while taking an antibiotic for another infection, your provider may tell you to stop taking it. Treatment may include a different type of antibiotic that targets C. diff bacteria, fluids if you are dehydrated, and possibly probiotics (though researchers are not sure if these supplements are helpful). If infections keep returning after treatment, talk with your provider about treatments that use good bacteria from the stool of healthy people to help control C. diff growth.
- Negative (normal): Generally means that no signs of a C. diff infection were found in your sample. Your symptoms are probably caused by something else. Limitation: A negative result on a C. diff toxin test alone is not enough to rule out a C. diff infection because C. diff toxins can break down quickly if your sample is not kept cool. For this reason, toxin tests are usually done with tests for C. diff toxin genes and/or C. diff GDH antigens. Next step: Your provider will consider other causes for your symptoms and may order additional tests.
- A negative result on a C. diff toxin test alone is not enough to rule out a C. diff infection because toxins can break down quickly if the sample is not kept cool.
- A GDH antigen test can show if C. diff is in your body, but it cannot tell if it is making you sick.
- After treatment for a C. diff infection, you will not be tested again to see if you are cured because it is common to still have C. diff in your body after you get better. A test would only show that the bacteria is still there, not whether you are likely to get sick again.
What to do next
If you have questions about your results and/or treatment, talk with your provider. To lower your chance of getting or spreading C. diff: avoid taking antibiotics you do not really need; let all your providers know if you have had a C. diff infection (including your dentist); wash your hands with soap and water every time you use the bathroom and before you eat anything. C. diff is contagious—people who have it spread it by not washing their hands before touching people and things that other people touch.
- What do my test results mean?
- Do I need any other tests?
- What treatment do you recommend?
- Should I stop taking any antibiotics I am currently on?
- How can I prevent spreading C. diff to others?