C. diff Testing

What is C. diff testing?

C. diff testing checks a sample of your stool (poop) for signs of an infection with bacteria called Clostridioides difficile (or C. diff).

C. diff are bacteria that live in your large intestine. There are multiple types of these bacteria. Some can live in your large intestine for years without making you sick. Others, however, can lead to infection if they grow out of control. If this happens, C. diff bacteria release toxins that irritate the lining of your colon (the biggest part of your large intestine) and cause digestive symptoms such as diarrhea.

In rare cases, a C. diff infection can cause more serious health problems such as toxic megacolon (when inflammation causes your colon to stop working) and a perforated bowel (when a hole forms in your intestinal wall). These are life-threatening conditions that need immediate treatment.

Most C. diff infections happen while you're taking certain antibiotics or within a few weeks after you finish taking them. That's because the antibiotics that kill harmful bacteria in your digestive system may also get rid of “good bacteria.” These bacteria help keep your digestive system healthy by helping to break down food and protect you from infections. If there are fewer good bacteria than usual, C. diff can grow out of control and make you sick.

You can also get a C. diff infection if you touch a surface with C. diff on it and then touch your mouth. That's because C. diff bacteria are common in the environment and in the stool of people who have these bacteria. So, 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.

However, if you're healthy and get C. diff from a contaminated surface, 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.

You can lower your chance of getting or spreading C. diff by:

• Not taking antibiotics that you don't really need.
• Letting 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.
• Washing your hands with soap and water every time you use the bathroom and before you eat anything.

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. There are various tests a health care provider can use to see if these bacteria are in your stool, including:

• Molecular tests, such as PCR tests. These look for genes from the types of C. diff that make toxins.
• Toxin tests. These check for two types of toxins called toxins A and B that certain types of C. diff bacteria create.
• Antigen tests. These look for certain proteins from C. diff bacteria called glutamate dehydrogenase (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 provider may order more than one type of C. diff test. They may also test for parasites and other bacteria to rule out other possible causes for diarrhea.

Why do I need C. diff testing?

You may need C. diff testing if you have symptoms and a high risk of an infection. Symptoms include:

• Watery diarrhea three or more times a day with no other known cause
• Abdominal (belly) pain
• Nausea
• Loss of appetite
• Fever
• Dehydration
• Colitis (inflammation in your colon)

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 these bacteria in your colon. It could begin to grow again and cause a new infection.
• Know you were exposed to C. diff.

Your provider may also use C. diff testing to:

• Help diagnose the cause of diarrhea after they've ruled out other potential causes
• Check for C. diff toxins if you've completed treatment and your symptoms come back

Testing usually isn't done to check for C. diff:

• If you don't have any symptoms. That's because to have an infection you need symptoms of one and C. diff bacteria in your stool.
• After treatment for an infection. 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 are still there, but not whether you're likely to get sick again.

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 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're unable to return the container right away, you should refrigerate your sample until you're ready to 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 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 genes that produce toxins or C. diff toxins. If you had a GDH test and your results show that there are GDH antigens in your stool, that doesn't necessarily mean you have an infection. Your provider will usually consider GDH test results along with the results from other tests.
• A negative (normal) test result generally means that no signs of a C. diff infection were found in your sample. Your symptoms may be the result of 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 if there are toxins in your digestive system. For this reason, toxin tests are usually done with tests for C. diff genes that produce toxins 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.