Tag Archives: What kind of specimen is tested for C-diff?

Clostridium difficile Diagnostic Testing Ranging From Most Sensitive to Lower End Sensitivity


Clostridium difficile Diagnostic Testing and C.diff. Background Information




According to the CDC statistic reporting 2015, there are 453,000 CDI cases diagnosed each year. 2/3 of the cases are Inpatient HAI only 24% have hospital onset, 23% Long-term care, 18% post discharge.

Rate of Colectomies have increased as high as 6.2% in epidemic periods.

CDI extends inpatient hospital stays by 2.3 to 12 days increasing financial burden by $2,454 to $27,160 EACH CASE.

More than 82% or 8 in 10 individuals are diagnosed with Community-associated CDI and had a recent healthcare exposure such as a Doctor’s office or Dentist office visit within 12 weeks time.

Each Year – 29k patients newly diagnosed with a CDI die within 30 days of a CDI (mostly senior population) 14k patients die each year from a CDI involvement.

Each Year – 83k patients are being treated for Recurrent CDI within 8 weeks of initial onset.

The most prevalent Clostridium strain today is the B1/NAP1/027 – the Hypervirulent Strain vs the 078 strain which was the typical strain.

027 Ribotype is the largest recorded outbreak and fatalities .  Mode of transmission remains the same – Fecal to Oral route transmission and lives on inanimate objects and surfaces longer than 6 months.

According to researchers Merrigan and colleagues (https://www.ncbi.nlm.nih.gov/pubmed/20675495)

Examined the accumulation of spores over the bacterial growth cycle and demonstrated that hypervirulent strains sporulated earlier and accumulated significantly more spores per total volume of culture than non-hypervirulent strains (078).  This increased rate of sporulation may explain the observation of unusually high relapse rates associated with hyupervirulent strains because patients are more likely to contaminate their local environment and subsequently re-infect themselves.  More research needs to be done to confirm this theory and it remains contentious.

Diagnostic Testing – Clostridium difficile (C.diff.):

There are a number of diagnostics and studies continue to create debate and discussions about CDI testing and diagnosis and the connection between testing methods and clinical outcomes.

Per studies and research by Dr.’s Dale Gerding, MD, Dr. M. Thomas, Jr.MD, Dr. Clifford McDonald in January 2016 the Diagnosis and Treatment of Clostridium difficile Infection   Gerding, Dale N. MD*†; File, Thomas M. Jr MD, MSc‡§; McDonald, L. Clifford MD

Infectious Diseases in Clinical Practice: January 2016 – Volume 24 – Issue 1 – p 3–10 doi: 10.1097/IPC.0000000000000350 NFID Clinical Updates

A 2006 survey found that the most common lab test for CDI diagnosis was EIA (Enzyme Immunoassay) for toxins A and B.  48-96 Hours turn around time. 

Found to generate false positives and false negative results.

Today PCR is by far the most common test. It became available for laboratory diagnosis C.diff. associated diarrhea (CDAD) and colitis in 2010.

>PCR = Polymerase Chain Reaction with a 1 day turn around.

>Proven sensitivity of 100%,,  96.9% A/B specific accuracy and superior to A/B EIA testing.

  • The MOST Sensitive test in use today is Culture plus Toxin Confirmation, but it is too SLOW to be of practical use.
  • Nucleic Acid Amplification Test –This test may lead to over diagnosing by detecting colonized patient with diarrhea from another cause (viral or other ).
  • Glutamate dehydrogenase EIA is very sensitive but not specific and cell cytotoxin is also too slow for practical use today.
  • At the lower end of sensitivity are toxins A and B EIA, toxin A  EIA,  GDH latex test, and endoscopy, which is approximately 50% sensitive.


If Labs have no clinical input and accept any unformed stool for testing, it may be most appropriate to use a test that better identifies CDI such as a relatively sensitive test for toxin in the stool (eg., cell cytotoxin or GDH = Glutamate dehydrogenase,  coupled with EIA for toxin).

If patients are screened carefully for clinical symptoms associated with a CDI (at least 3 unformed stools within 24 hours plus a history of antibiotic therapy) then a highly sensitive test such as the NAAT or a toxigenic culture, or GDH plus toxin detection may be best.

Neither approaches have been established today – appropriate testing strategy remains a dilemma.

Clinicians should be aware of the test being used in their laboratories. 

 >If a NAAT = Nucleic Acid Amplification Test  (PCR=Polymerase Chain Reaction or LAMP = Loop Mediated Isothermal Amplification) is being used, then they should recognize the potential for over diagnosis, especially if the specimens are sent from patients with minimal diarrhea.

>If EIA toxin testing is being used, it is more likely that a positive test represents CDI, but EIA testing yields FALSE negatives in patients with CDI due to the lack of sensitivity.

A less complicated breakdown of diagnostic testing:

Cultures:  Stool culture for C. diff.  most sensitive test available. 48-96 hours turn around.

Molecular tests:  FDA approved PCR assays, test for the gene encoding toxin B, are highly sensitive and specific for the presence of a toxin-producing Clostridium difficile organism.

Antigen detection:  rapid tests – less than 1 hour – detect presence of C. diff. antigen by latex agglutination or Immunochromatographic assays.  (used often in ER).

Toxin testing – tissue culture cytotoxicity assay detects toxin B only. Costly and requires 24-48 hours for final result. Historical gold standard for diagnosing clinical significant disease caused by C. diff. it is recognized as less sensitive than PCR or culture for detecting the organism in patients with CDI symptoms.

Enzyme immunoassay detects toxin A , toxin B  or both A and B.  Due to concerns overtoxin A-negative, B-positive strains causing disease, most laboratories employ a toxin B only or A and B assay.  Because these are same day assays that are relatively inexpensive and easy to perform, they are popular with clinical labs. There are increasing concerns about their relative insensitivity – less than tissue culture cytotoxicity and much less than the PCR or toxigenic culture.

C. diff. toxin is very unstable. The toxin degrades at room temperature and may be undetectable within 2 hours after collection of a specimen.

False-negative results occur when specimens are not properly tested or kept refrigerated until the testing can be done.

To learn more about how to collect and transport stool specimens to the laboratory click on the link below: