C. diff. Testing and Diagnosis

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Bobbie
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C. diff. Testing and Diagnosis

Postby Bobbie » Thu Aug 19, 2010 1:07 pm

Beth donated this info. Thanks, Beth and also Kitabeck, who described the same testing.

The hospital where I tested negative, does not test for toxin A anymore. They have this new, very sensitive test where they test the sample by "real-time polymerase chain reaction (PCR) by Cepheid GeneXpert) for the presence of the c difficile toxin B gene (tcdB). " They use the company Cepheid, but I looked online and Arup labs also has similar tests. At first, I was sure that it was not as good a test as the one that tests toxin A and B, but after speaking to ID docs and my GI I was told that this one is much more sensitive and is meant to distinguish c diff that is harmful and toxigenic. They found that they were overtreating people who tested positive on the older tests. Some believe that toxin A should not be treated unless symptoms get much worse.
Last edited by Bobbie on Wed Mar 04, 2015 2:50 am, edited 4 times in total.
Reason: updating

Bobbie
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Re: Tests - C. Diff. (Latest Info. is Listed Last)

Postby Bobbie » Tue Nov 15, 2011 4:12 pm

mray posted this information. Thanks.

The PCR test doesn't look for C Diff, it looks for a piece of DNA, the DNA that codes for toxin B. Polymerase Chain Reaction is a very power molecular technique that amplifies DNA so that it is more easily detected. That's what it does.

It's true, if C diff is at a very low level, it probably won't pick it up, there is a limit to the resolution. Also, if you are a carrier, it probably won't be detected. However, in those situations, C Diff most likely wouldn't be causing you symptoms.

The test, however, is dependent on proper handling by the patient and the lab. Also, lots of mucous or blood might affect the PCR technique, BUT, there is a built in control in most of the PCR kits to account for that. Also, if you are on antibiotics, it's not going to be reliable either.

So, if you have a number of negative PCR tests, and you have symptoms, you might want to look into something else.

Bobbie
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Re: Tests - C. Diff. (Latest Info. is Listed Last)

Postby Bobbie » Tue Nov 15, 2011 4:16 pm

mray posted this information. Thanks.


For the most part, PCR only tests for the toxin B gene. I believe there is a kit that tests for toxin B gene, and another random gene from C Diff, but not toxin A. The most popular PCR kit only tests for the toxin B gene and nothing else.

There are strains of C Diff that only produce toxin B. I don't believe there are strains that produce only toxin A that cause much trouble.

The idea is that if there is no toxin B gene, there is no C Diff disease.

There isn't much point to doing the old toxin A&B test anymore. The PCR test is more sensitive and has a greater negative predictive value.

Bobbie
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Re: Tests - C. Diff. (Latest Info. is Listed Last)

Postby Bobbie » Tue Nov 15, 2011 4:25 pm

Most lab techs. told me speciman shold be in a STERILE (not just clean) container and be refrigerated immediately unless tested right away. One lab tech told me when labs are really busy, they sometimes remove many specimans from the refrigerator and let them "sit." Mark your container: CDIFF - TEST IMMEDIATELY on the top in red.

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Re: Tests - C. Diff. (Latest Info. is Listed Last)

Postby Bobbie » Wed Jan 11, 2012 4:38 pm

I wanted to provide this info re PCR test. Be sure to use a STERILE not just a clean cup. Test is about 90% accurate - much more so than previous tests. Turn into lab within 24 hours - keep refrigerated.

Mark on top of speciman; "C. Diff testing - refrig. or test ASAP." initial results within 24 hours - final results takes 3 days. I got this info. directly from a "lab engineer" who told me, "I wish nurses would stop telling people 'clean' containers are OK."

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Re: Tests - C. Diff. (Latest Info. is Listed Last)

Postby Bobbie » Sat Mar 24, 2012 3:20 pm

Postby Bobbie » Fri Jan 20, 2012 1:04 am

i haven't had to do a stool sample since l999. recently i had to take a speciman in to a hospital lab. they denied it -- not 'watery' enough although i talked to a lab tech who said - from my description, it should be ok. the lab denied the sample, they contacted my gi's office who neglected to tell me until i called to check.

Labs employ both lab techs and lab engineers. Lab engineers are the ones who make the decisions. i found a great one and she said my second sample was OK. i got her supervisor's name so i can compliment her; she seemed to be the only one there who really knew what she was doing.

Be sure you use a STERILE not just a clean container.

Per lab engineer re. PCR test:

Sample has to be a certain "consistency" before labs here will do the PCR test. Here's the "real scoop" (or I could say poop) per a "lab engineer" (they do the actual testing). If a stick will stay upright in a sample, it's not acceptable for the test.

I'm sure different labs have different regulations.

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More info. re. PCR

Postby Bobbie » Sat Aug 11, 2012 5:42 pm

C. diff. expert says:

PCR for CDI remains positive ( DNA only) for 2-3 weeks after successful FMT,
Culture and toxin go negative immediately

Bobbie
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Re: Tests - C. Diff. (Latest Info. is Listed Last)

Postby Bobbie » Sat Mar 16, 2013 4:32 pm

roy » Sat Mar 16, 2013 1:41 pm

False positives are fairly common even with PCR
Toxin can remain in the colon after the C.diff has been killed, also dead C.diff still has DNA!

http://ricn.on.ca/cdifficilefaqsc3551.php
Take a look at paragraph 9

Bobbie
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Re: Tests - C. Diff. (Latest Info. is Listed Last)

Postby Bobbie » Sat Mar 16, 2013 4:36 pm

Should you test to see if you are cured?

Roy contributed this information.

http://www.dhh.state.la.us/offices/misc ... Manual.pdf

http://www.cdc.gov/ncidod/dhqp/pdf/infD ... M02_06.pdf

http://www.cap.org/apps/cap.portal?_nfp ... bel=cntvwr

There's plenty of info here that Drs should already know but don't seem to!

Often a Drs enthusiasm to treat causes HARM.

Read the section in the third link about asymptomatic carriage rates where treatment might not be needed. That link is the Collage of American Pathology.

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Re: Tests - C. Diff. (Latest Info. is Listed Last)

Postby Bobbie » Thu Oct 10, 2013 3:19 pm

Re: Lab won't test

Postby roy » Thu Oct 10, 2013 1:10 pm

A Dr CAN OVERIDE the lab and ask for a test on solid stool, it has to be specified as a c.diff test on solid stool on the request form.
The reason has to be stated ( long term intermittent diarrhoea )

Bobbie
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Re: Tests - C. Diff. (Latest Info. is Listed Last)

Postby Bobbie » Tue Apr 08, 2014 11:33 pm

Roy submitted this about freezing samples.

http://www.stanfordlab.com/LabTestGuide ... ?ID=CDTPCR

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Re: C. diff. Testing (Latest Info. Listed Last)

Postby Bobbie » Sun Jul 13, 2014 9:45 pm

CDC REPORT (Page last updated: March 26, 2014)
Content source: Centers for Disease Control and Prevention

This is a detailed report on HAI's (hospital acquired infections), including C. diff. and in-depth information on testing and why toxin tests are often inaccurate. Be sure and read so you will know what questions to ask your doctor and which tests are best.

During my first bout of C. diff. (l993-l997), I only tested positive on the toxin test several times although I was diagnosed with pseudo. memb. colitis by a colonoscopy. Was also misdiagnosed at Mayo in l993 - was on Vanco. - which they knew - so tests were negative. Evidently, they didn't know then that Vanco. (also Flagyl and I'm sure Dificid) can affect test results.

http://www.cdc.gov/HAI/surveillance/index.html

Also, see the ABC Bibles in CDI and another report from the CDC in CDI - Contact Info.

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Re: C. diff. Testing (Latest Info. Listed Last)

Postby Bobbie » Sun Jul 13, 2014 9:47 pm

A C. diff. expert advises retesting should be done only if there are symptoms and after being off Vanco./Flagyl/Dificid for 10 to 14 days.

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False Positive Testing

Postby Bobbie » Sat Dec 06, 2014 4:31 pm

Roy submitted this info.

Re: False Positive testing.

Go to this link
Scroll down to mirobiology and diagnosis
read it all including the recommendations under "timing of assays"

http://gi.org/guideline/diagnosis-and-m ... d-colitis/

Bobbie
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Re: C. diff. Testing - Includes Recent CDC Report

Postby Bobbie » Sat Dec 06, 2014 4:42 pm

Roy donated this info.

Ordering 3 tests is about 4 years out of date!
It comes from the bad old days when tests were seriously unreliable!!
Todays PCR tests are much better.
Trouble with multi tests is what one is correct?
Test 10 times and on average one will be wrong!
What's right the one positive or the nine negative?
Multi tests are not recommended!


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