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C. diff Testing

What is C. diff testing?

C. diff testing checks a sample of your stool (poop) for signs of an infection with a bacteria called C. diff. C. diff is also called C. difficile or Clostridioides difficile. It used to be called Clostridium difficile.

A C. diff infection affects your large intestine. It can cause symptoms that range from mild diarrhea to serious dehydration and colitis (inflammation in your colon, which is the biggest part of your large intestine). In rare cases, a C. diff infection can become life-threatening.

C. diff bacteria are common in the environment, and it's in the stool of people who have the bacteria. If a person with a C. diff infection doesn't wash their hands well after using the bathroom, tiny amounts of contaminated stool can get on anything or anyone that they touch.

You can get the bacteria if you touch a contaminated surface and then touch your mouth. But if you're healthy, you usually won't get sick. Good bacteria in your digestive system will prevent the C. diff from growing out of control and causing an infection.

Most C. diff infections happen while you're taking certain antibiotics or within weeks after you finish taking them. That's because the antibiotics that kill bad bacteria may also get rid of good bacteria in your digestive system that help prevent infections. If your good bacteria are gone, C. diff can grow out of control and make you sick.

When C. diff grows, it can release toxins that irritate the lining of your colon and cause symptoms. Some C. diff tests check your stool sample for these toxins. Other tests check for genes from the types of C. diff that make toxins. Some types of C. diff don't make toxins or cause illness.

There are also tests that look for certain proteins from C. diff bacteria called GDH antigens. GDH antigen tests can show if you have C. diff in your body. But they can't tell if it's making you sick. To make an accurate diagnosis, your health care provider may order more than one type of C. diff test.

Other names: C. difficile, Clostridium difficile, Glutamate dehydrogenase test GDH Clostridioides difficile, C. difficile toxin test, C. difficile culture, antibiotic-associated pseudomembranous colitis, C. difficile toxin, PCR

What is it used for?

C. diff testing is most often used to find out if C. diff is causing diarrhea. But diarrhea can have many causes, so the test may be used with tests for parasites and other bacteria that also cause diarrhea.

Why do I need C. diff testing?

You may need C. diff testing if you have symptoms of an infection. The main symptoms of a C. diff infection include:

It is especially important to be tested if you have symptoms and you have a high risk of getting a C. diff infection. Your risk is high if you:

  • Have taken antibiotics within the last six to eight weeks.
  • Are aged 65 or older.
  • Have recently stayed in or worked at a hospital, nursing home, or other health care facility. C. diff bacteria are more common in health care facilities.
  • Have a weakened immune system from a health condition such as HIV or certain medicines or treatments, including chemotherapy for cancer.
  • Had C. diff in the past. After you recover from a C. diff infection, you may still have the bacteria in your colon. It could begin to grow again and cause a new infection.
  • Know you were exposed to C. diff.

What happens during C. diff testing?

You will need to provide a fresh sample of loose or liquid stool for your test. Your provider will probably give you a container or kit with instructions on how to collect the sample. There are different ways to collect the stool samples so follow the instructions carefully. In general, you'll need to:

  • Label the container with your name, the collection date, and time.
  • Collect a stool sample as instructed. This usually involves using a clean, dry container, or special paper or plastic wrap placed over the toilet to catch the stool.
  • Make sure the stool doesn't mix with any urine, toilet paper, or water from the toilet.
  • Close the container tightly.
  • Wash your hands well with soap and water.
  • Return the container according to the instructions. This is important to get an accurate test result. If you are unable to return the container right away, you should refrigerate your sample until you're ready deliver it.

If you're collecting a sample from diapers, you'll get special instructions for using plastic wrap inside of a clean diaper. In certain cases, a provider may use a swab to take a stool sample from the rectum.

Will I need to do anything to prepare for the test?

You don't need any special preparations for C. diff testing.

Are there any risks to testing?

There is no known risk to having C. diff testing.

What do the results mean?

There are several tests for C. diff that check for different signs of infection in your stool sample. Your provider may order a combination or 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.

In general:

A positive (abnormal) test result 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. These are genes from the types of C. diff that can cause illness.
  • C. diff toxins. These tests check for two types of toxins called A and B.

A negative (normal) test result generally means that no signs of a C. diff infection were found in your sample. Your symptoms are probably caused by something else.

But a negative result on a C. diff toxin test alone isn't enough to rule out a C. diff infection. That's because C. diff toxins can break down quickly if your sample isn't kept cool. If this happens, a toxin test may not find toxins in your sample, even when they're making you sick. For this reason, toxin tests are usually done with tests for C. diff toxin genes and/or C. diff GDH antigens.

If you're diagnosed with a C. diff infection while you're taking an antibiotic for another infection, your provider may tell you to stop taking it. Your treatment may include:

  • Taking a different type of antibiotic that targets C. diff bacteria
  • Fluids if you are dehydrated

Some people may take probiotics, a type of supplement that might support good bacteria in your digestive system. But researchers aren't sure if these supplements are helpful.

If C. diff infections keep returning after treatment, talk with your provider. There are treatments that can help reduce the chance that C. diff will come back. These treatments use good bacteria from the stool of healthy people to help control the growth of C. diff.

If you have questions about your results and/or treatment, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about C. diff testing?

After treatment for a C. diff infection, you won't be tested again to see if you're cured. That's because it's common to still have C. diff in your body after you get better. A test would only show that the bacteria is still there, but not whether you're likely to get sick again.

To lower your chance of getting or spreading C. diff:

  • Avoid taking antibiotics that you don't really need.
  • Let all your providers know if you've had a C. diff infection, including your dentist. This information will help them make decisions if you need antibiotics in the future.
  • 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.


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The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.