What's the Typical Workup for Diagnosing C. Difficile Infection?

MAY 08, 2018
MD Magazine Staff

Peter Salgo, MD: If you want to start working these patients up, what are the first tests that you use?

Yoav Golan, MD: It depends on the test that you have available to you, obviously. If you think that someone qualifies for Clostridium difficile [C. diff]—they have enough diarrhea, at least 3 loose stool bowel movements a day, and they don’t have any other explanation for the diarrhea—it depends on your lab. There are 2 types of testing methodologies that are being used. Most labs now use PCR [polymerase chain reaction]–based testing. Some labs still recommend 2-step testing with glutamate dehydrogenase. Toxin testing, first, and PCR as a second...

Peter Salgo, MD: These are stool tests?

Yoav Golan, MD: These are all stool tests.

Peter Salgo, MD: Nobody is getting blood tests?

Yoav Golan, MD: There are no blood tests for C. difficile. These are all stool tests. There are 2 methodologies for doing the stool tests.

Peter Salgo, MD: We have tests that detect free toxin genes, right? We have tests that target the toxins themselves, or detect the presence of strains with the potential to produce toxins. Can you kind of sort that out for me?

Dale N. Gerding, MD: The detection of the organism, which is most of the focus in US hospitals—about 80% of them are using a PCR testing modality. We call it NAAT—nucleic acid amplification testing, which detects the toxin genes, sometimes misreported as detecting the toxin. It isn’t actually detecting toxins. It’s only detecting the DNA of the toxin genes.

Peter Salgo, MD: They’re engaged to be engaged.

Dale N. Gerding, MD: That’s it. The other aspect of testing actually tests the presence of the toxin itself in the stool. This is thought to be the more specific test. There is a great debate going on right now about whether PCR or NAAT testing is too sensitive—picking up the organism in patients who might just be colonized but may have diarrhea because somebody gave them a laxative, or they went on tube feedings, or for whatever other reason.

Peter Salgo, MD: That’s almost guilt by association. If you have diarrhea and you find the organism, the temptation is to say, “Whoa, C. diff. You’re telling me, maybe not?

Dale N. Gerding, MD: I’ve never seen a house staff member who could resist a positive test.

Yoav Golan, MD: You send the test. You get the test result, and then you say, “Well, despite the fact that I suspected it and sent the test and the test is now positive, I’m not going to treat.” The tricky and most important thing is to decide who to test. Because once you send a test, even if the patient may be colonized, it’s very hard to resist therapy. And so, it’s really critical to decide who to test, which goes back to our previous discussion.

Peter Salgo, MD: It goes back to what you were saying. In other words, if you’ve been giving somebody who has diarrhea lactulose, don’t send the C. diff test, if I hear you correctly, until you’ve stopped the driver and see what happens. Now, if somebody is on lactulose with a white count of 50,000, and he or she has diarrhea, that’s a different story.

Darrell S. Pardi, MD: Right. That comes back to what do you—or, more importantly, what does the patient have to lose? If they’re on lactulose or a laxative, and they’re having 12, 15 bowel movements a day, and the white blood cell count is 50, you probably should test for C. diff. You may even start empiric therapy while you’re waiting for the test to come back, rather than stopping the lactulose to see how they do. They have a lot to lose.

Transcript edited for clarity.
 

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