Lab Test

C. difficile GDH/Toxin

Clostridium difficile, C diff, Toxin A, Toxin B, Antibiotic associated diarrhea, hospital acquired diarrhea, healthcare associated diarrhea, CDAD, CDI, tcdA, tcdB, gene, GDH antigen, psuedomembranous colitis

Test Codes

EPIC: LAB7110

Department

Microbiology

Specimen Collection Criteria

Collect: One of the following specimens:

  • Liquid or soft stool in a sterile collection container without preservatives. Stools that do not conform to the shape of the container with not be tested.
  • Random stool specimen placed in a container with Para-Pak/Cary-Blair transport medium.

Physician Office/Draw Specimen Preparation

Stool in a sterile collection container, refrigerated (2-8°C or 35-46°F).
Stool specimen in Para-Pak/Cary-Blair medium, room temperature (20-26°C or 68-78.8°F).

Preparation for Courier Transport

Transport: Stool in a sterile collection container, refrigerated (2-8°C or 35-46°F). Stool specimen in Para-Pak/Cary-Blair medium, room temperature (20-26°C or 68-78.8°F).

Rejection Criteria

  • Stool aspirates or endoscopic procedures
  • Specimens placed in any type of transport medium or preservative other than Para-Pak/Cary-Blair transport medium.
  • Specimens un-refrigerated for greater than 24 hours.
  • Specimens refrigerated for greater than 3 days.
  • Specimens submitted on a swab.
  • Stool that does NOT conform to the shape of the container.
  • Stool received in non-approved containers (diapers, other household containers, etc.).
  • Stool specimens that had a previous test within 7 days.
  • Stool specimens that had a positive result within the previous 14 days (inpatient only).

In-Lab Processing

Samples should be tested within 24 hours of collection. 

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 24 hours
Refrigerated (2-8°C or 36-46°F): 3 days
Frozen (-20°C/-4°F or below): 30 days

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Dearborn Microbiology Laboratory
Canton, Taylor, Trenton and Wayne sent to Dearborn Microbiology Laboratory for testing.

Farmington Hills Microbiology Laboratory
Livonia sent to Farmington Hills Microbiology Laboratory for testing.

Royal Oak Microbiology Laboratory
Grosse Pointe sent to Royal Oak Microbiology Laboratory for testing. 

Troy Microbiology Laboratory
Lenox sent to Troy Microbiology Laboratory for testing.

Performed

Sunday – Saturday, 3-4 times daily.
Results available within 8 hours of receipt in the Laboratory. Results for specimens requiring nucleic acid amplification reflex testing will be delayed by up to 8 additional hours.

Reference Range

Negative.

Test Methodology

Membrane enzyme immunoassay – FDA Approved (Quik Chek Complete, Alere)

Reflex nucleic acid amplification – FDA approved (BD MAX Cdiff, Becton Dickinson; Xpert C.difficile; Cepheid/Danaher).

Interpretation

By report. The most common resulting scenarios are as follows:

  • GDH (negative), Toxin A/B (negative), NAA (not performed):
    NEGATIVE – toxin producing C. difficile not detected. It is unlikely that the patient has C. difficile.

  • GDH (positive), Toxin A/B (positive), NAA (not performed):
    POSITIVE – toxin producing C. difficile detected. The patient likely has C. difficile infection.

  • GDH (positive), Toxin A/B (negative), NAA (not performed):
    INDETERMINATE – Non-toxin producing C. difficile detected. If clinically suspected to have active C. difficile infection, consider empiric therapy and consultation with Infectious Diseases.

  • GDH (negative), Toxin A/B (positive), NAA (positive):
    POSITIVE – toxin producing C. difficile detected. Test results are indeterminant. The patient may be colonized with toxigenic C. difficile; infection cannot be excluded. Suggest consultation with Infectious Diseases.

  • GDH (negative), Toxin A/B (positive), NAA (negative):
    INDETERMINATE – test results are incongruent. Interfering substances are likely producing a false positive Toxin A/B result. Submit another stool sample for testing if clinically indicated.

LIMITATIONS:

  1. False Negative results may occur due to the following:
    • Improper specimen collection, handling, and/or storage
    • Presence of inhibitory substances
    • Antigen, toxin or toxin gene quantity in the stool is below the limit of detection
  2. False Positive results may occur due to the following: 
    • If present in the stool, Clostridium sordellii VPI 9048 produces both HT(hemorrhagic toxin) and LT (lethal toxin) which share high DNA and amino acid sequence homology to C. difficile Toxins A and B, respectively.

Clinical Utility

This test aids in the qualitative detection of toxigenic C. difficile in human liquid or soft stool specimens from patients suspected of having Clostridium difficile-associated disease (CDAD). Testing begins with the simultaneous detection of C. difficile antigens glutamate dehydrogenase (GDH) and Toxin A/B. If both test components are negative or positive, no further testing is required. Reflex NAA testing for the Toxin A or B gene is automatically performed with GDH (negative) and Toxin A/B (positive) results.

Clinical Disease

C. difficile, a Gram-positive, anaerobic, spore-forming bacillus, is recognized as the primary etiologic agent of hospital associated diarrhea, and is responsible for approximately 20% of cases of antibiotic-associated diarrhea and the vast majority of cases of pseudomembranous colitis. Symptoms of C. difficile infection (CDI) include watery diarrhea, pseudomembranous colitis, fulminant colitis and even death.

Epidemiology

  • C. difficile is the primary etiologic agent of hospital associated diarrhea, and is responsible for approximately 20% of cases of antibiotic-associated diarrhea and the vast majority of cases of pseudomembranous colitis. The incidence of C. difficile infection (CDI) has steadily increased over the last decade. Concomitantly, the organism has become more virulent and more difficult to treat, inciting a tremendous financial burden to health care facilities estimated in excess of $1 billion annually.
  • Common risk factors for acquisition of CDI include age, length and number of hospital stays, invasive medical procedures, and utilization of certain antibiotic and/or anti-neoplastic chemotherapeutic agents.

Incubation Period

Variable (days to months).

Transmission

Fecal-oral route. Spores, not viable (vegetative) cells are the primary means of acquisition and transmission. These are ubiquitous in health care facilities and the environment. The spores are extremely resilient, requiring high-level disinfection.

Reference

Common Scenarios Necessitating Test Cancellation 

Cancellation Scenario Applies to Outpatients Applies to Inpatients
Formed Stool Yes Yes
7 Day Rule Yes Yes
14 Day Rule Not Applicable Yes

  • Formed Stool: C. difficile is a diarrheal illness. Testing will only be performed on stool that conforms to the shape of the collection container. 
  • 7 Day Rule: A positive or negative C. difficile test was obtained within the last 7 days. Repeat testing during the same episode of diarrhea or for "test of cure" is not recommended.
  • 14 Day Rule: A positive C. difficile test was obtained within the last 14 days. Repeat testing is not recommended as the test may remain positive despite effective therapy and symptom resolution. In addition, subsequent testing that yields a positive test result artificially increases the nosocomial infection rate as reported to the National Healthcare Safety Network (NHSN).

Note:  Exceptions to these rules will be decided on a case-by-case basis. Please contact the Medical or Technical Director of the Microbiology Laboratory.

CPT Codes

87449, 87324, 87493 (reflex NAA)

Contacts

Last Updated

7/29/2022

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