Clostridioides difficile infection (CDI) is an acute diarrheal illness caused by a toxin producing anaerobic gram-positive, spore forming bacilli. Patients may be exposed to this organism in the environment or health care setting such as hospitals or long term care facilities. CDI is caused when the normal microbial flora is disrupted due to antibiotic use or through other causes such as abdominal surgery or the use of proton pump inhibitors enabling this organism to proliferate in the colon causing an acute colitis.

The two toxins produced by C. difficile are toxin A, an enterotoxin, and toxin B, a cytotoxin. These toxins cause an acute inflammatory response resulting in a spectrum of symptoms ranging from mild self-limiting diarrhea to bloody mucous diarrhea, pseudomembranous colitis and in extreme cases toxic megacolon. It is important to note that not all C. difficile strains are toxin producing and that non-toxigenic strains do not cause CDI.

The diagnosis of CDI is based on the presence of clinical symptoms defined as the presence of ≥ 3 watery, loose, or unformed stools within a 24-hour period coupled with a positive laboratory test on a stool specimen.

Laboratory testing for CDI

This usually involves a multi-step test algorithm involving testing the stool specimen for the presence of glutamate dehydrogenase (GDH) antigen and toxins A and B produced by C. difficile using an enzyme immunoassay (EIA). Any discrepant result between the GDH antigen and toxins is resolved by a molecular test such as a polymerase chain reaction (PCR).

LifeLabs Ontario will offer an Enzyme Immunoassay (EIA) test for the diagnosis of C. difficile infection, starting in January 2022.

LifeLabs is happy to announce that it will be offering the Clostridium difficile Enzyme Immunoassay Screen test for community patients in Ontario. This test will be covered by Ontario Health Insurance Plan (OHIP).

LifeLabs will use the TECHLAB^® C. DIFF QUIK CHEK COMPLETE® rapid membrane enzyme immunoassay for the simultaneous detection of GDH antigen and toxins A and B.

This test has a high specificity and when the GDH antigen and toxins A/B are both positive or both negative a confirmatory test is not required improving the turnaround time of results.

This test detects C. difficile GDH antigen as a screen for the presence of C. difficile and confirms the presence of toxigenic C. difficile by detecting toxins A and B in fecal specimens.

The test uses antibodies specific for C. difficile GDH antigen and toxins A and B to detect the antigen and toxins in fecal specimens of patients suspected of having CDI.

Any discrepant or invalid EIA result will be confirmed by a Nucleic Acid Amplification Test (NAAT). At LifeLabs we use the Polymerase Chain reaction (PCR) NAAT test performed on the BD MAX^TM system which detects the C. difficile toxin B gene(tcdB) to confirm discrepant EIA results.

Results should be interpreted in correlation with patient history and clinical examination.

A test of cure is not indicated.

Ordering:

The C. difficile EIA test can be ordered by writing ‘C. diff EIA Screen Test’ on the ‘Other Tests’ section of the standard Ontario MOH requisition form.

Samples without a signed requisition by a physician will not be accepted.

Sample Collection and Transport:

The patient must collect 5-10 ml of liquid or soft stool in a labelled 90 ml sterile container and drop it off at any LifeLabs Patient Service Center (PSC) in Ontario.

Store and ship specimen at 2 – 8°. If delayed >72 hours from the time of collection, freeze sample at -20°C.

Please note: Optimal results are obtained when specimens are stored and shipped at 2-8°C and testing done within 72 hours of collection.

Freezing and thawing of the specimens may result in suboptimal results.

Reasons for Sample Rejection:

• Formed stool (stool does not take the shape of the container)
• Stool collected ≤ 7 days from a previously positive specimen
• Specimens submitted in preservative like SAF or Cary-Blair
• Stool specimen from a child ≤ I year of age
• Insufficient stool specimen received
• Rectal swabs

Turn Around Time, Result Reporting:

Results will be available to the ordering physician within 48-72 hours of specimen drop off.

• A Positive result will be reported as ‘Clostridioides (formerly Clostridium) difficile GDH antigen and toxin detected by Rapid Membrane Enzyme Immunoassay. Results must be interpreted based on clinical findings and are supportive of C. difficile infection (CDI). Repeat stool submitted within 7 days will be rejected.’
• A Negative result will be reported as ‘Clostridioides (formerly Clostridium) difficile GDH antigen and toxin not detected by Rapid Membrane Enzyme Immunoassay. Results are not supportive for diagnosis of C. difficile infection (CDI). Repeat stool submitted within 7 days will be rejected.’
• There can be two reasons for an Indeterminate/Discrepant result. These will be reported as:
  • ‘Clostridioides (formerly Clostridium) difficile GDH antigen detected, Toxin A and B not detected by Rapid Membrane Enzyme Immunoassay
    Sample referred for confirmatory testing’

  • ‘Clostridioides (formerly Clostridium) difficile A and B toxin detected, GDH antigen not detected by Rapid Membrane Enzyme Immunoassay
    Sample referred for confirmatory testing’
• The result of a specimen Confirmed Positive by PCR testing will be reported as ‘Clostridioides (formerly Clostridium) difficile toxin B gene (tcdB) DNA detected by nucleic acid amplification. Repeat stool submitted within 7 days will be rejected.’
• The result of a specimen Confirmed Negative by PCR testing will be reported as ‘No Clostridioides (formerly Clostridium) difficile toxin B gene (tcdB) DNA detected by nucleic acid amplification. Repeat stool submitted within 7 days will be rejected.’

For any questions, please contact our Customer Care Centre at 1-877-849-3637

 Yasmeen M Vincent, MBBS, MD
Medical Microbiologist,
LifeLabs ON

David Fenton, BSc, MLT
Technical Quality Specialist- Molecular Diagnostics
LifeLabs ON