Sanford Laboratories is pleased to announce that effective March 1st, 2016, we will be offering an additional test
to assist in the diagnosis of Clostridium difficile infection (CDI). This test is a two-step algorithm and is an aid to
answering the challenge of diagnosing CDI. The two-step algorithm optimizes the laboratory diagnosis of CDI by
providing first the sensitivity of PCR to capture those patients who have the gene for toxigenic C. difficile, and
second, the specificity of the toxin immunoassay to detect the presence of C. difficile toxin in the patient stool.
Below is a diagram of how the two step algorithm works when ordering the C. difficile toxin B by NAD, reflex to
Toxin A/B test.
Step 1
Step 2
PCR
Positive
Perform
immunoassay
for toxin
detection.
PCR
Negative
No further
testing
necessary.
PCR is
Performed
Immunoassay
positive.
Indicates toxin
detected.
Immunoassay
Negative.
Indicates no
toxin detected.
The two-step algorithm has been discussed in the literature as optimal testing to provide laboratory data to
support the diagnosis. PCR assays when positive detect the toxigenic organism rather than the toxin in the stool.
The carriage rate of C. difficile in asymptomatic adults has been reported to vary from 3% to 15%. PCR does not
discern between carriage and infection and therefore, by adding the immunoassay for toxin detection, the
laboratory provides an optimized assay to aid the provider in their clinical diagnosis of CDI.
To order the two-step algorithm:
Test Name:
Test Code:
CPT:
Specimen:
Transport:
Test TAT:
C. difficile toxin B by NAD, reflex to A/B Toxin Detection
*NBLD0538
87493, 87324
2-3 grams of liquid or very soft stool in a dry sterile container. Testing will only be performed on
diarrheal stools based on the Bristol Stool Chart 5, 6, and 7 specimens.
Send specimens refrigerated up to 3 days and frozen if greater than 3 days
Daily
*Rapid City clients please order test code: NBLD0540 - C.difficile Toxin DNA, reflex to A/B Toxin Detection
These tests are also available separately for those of you who wish to optimize your own facilities’
testing with the second step process:
Test Name:
Test Code:
CPT:
Specimen:
Transport:
Test TAT:
Test Name:
Test Code:
CPT:
Specimen:
Transport:
Test TAT:
Test Name:
Test Code:
CPT:
Specimen:
Transport:
Test TAT:
C. difficile Toxin B by Nucleic Acid Detection (NAD)
NBLD0386
87493
2-3 grams of liquid or very soft stool in a dry sterile container. Testing will only be
performed on diarrheal stools based on the Bristol Stool Chart 5, 6, and 7 specimens.
Send specimens refrigerated up to 3 days and frozen if greater than 3 days
Daily
C. difficile Toxin DNA (Rapid City)
NBLD0413
87493
3-5 grams of liquid in dry sterile container. Testing will only be performed on diarrheal
stools based on the Bristol Stool Chart 5, 6, and 7 specimens.
Send specimens refrigerated up to 5 days and frozen if greater than 5 days
Daily
C. difficile Toxin A/B
NBLD0224
87324
2-3 grams of liquid or very soft stool in a dry sterile container. Testing will only be
performed on diarrheal stools based on the Bristol Stool Chart 5, 6, and 7 specimens.
Send specimens refrigerated up to 3 days and frozen if greater than 3 days
Daily
References:
Optimizing the Laboratory Diagnosis of Clostridium difficile Infection. Peter H. Gilligan. Clin Lab Med 35 (2015)
299-312.
Overdiagnosis of Clostridium difficile Infection in the Molecular Era. Polage CR eta al. JAMA Intern Med. 2015
Sep 8:1-10.
Differences in outcome according to Clostridium difficile testing method: a prospective multicenter diagnostic
validation study of C. difficile infection. Timothy Planche et al. Lancet Infect Dis 2013:13: 936-945