Stool: Clostridium difficile common antigen and toxin/toxin gene

CT1811A: Positive/Positive     CT1811B: Negative/Negative


CT1811-A: C.difficile common antigen positive and gene/toxin positive viable for 56 days

CT1811-B: C.difficile common antigen negative and gene/toxin negative, viable for 57 days

Reference Laboratories

CT811-A: 12/12 laboratories reported toxin/toxin gene positive (9/12 also reported common antigen positive while 3 did not test)

CT811-B: 11/12 laboratories reported toxin/toxin gene negative (1 lab reported common antigen negative and did not test for toxin).

Participants’ results

NOTE: grading for Clostridium difficile toxin testing has changed. Please click here for more details

Table 1. CT1811A - Antigen/Toxin or Toxin geneTotalGrade
Positive/ Positive48Acceptable/Acceptable
NT / Positive10Ungraded/Acceptable
Negative/ Negative1Unacceptable/Unacceptable

Table 2. CT1811A - IC /PH NotificationTotalGrade

Table 3. CT1811B - Antigen/Toxin or Toxin geneTotalGrade
Not tested/Negative10Ungraded/Acceptable
Negative/Not tested4Acceptable/Ungraded

NT: not tested

Suitability for Grading

A challenge is considered suitable for grading if agreement is reached by 80 percent of selected reference group and at least 70 percent of the participants.

Antigen and toxin detection was correctly performed by at least 80 percent of reference laboratories and greater than 70 percent of all laboratories thus, both challenges were determined to be suitable for grading.

Grading: Please note that grading for Clostridium difficile toxin testing has changed. Please click here for more details

The samples are assessed for homogeneity and stability using in-house quality control methods and random selection of samples before and during production, and post sample delivery. The number of random samples selected is based on selection tables within Military standard 105E (1).

The challenge sample lot was confirmed to be homogeneous and stable for at least 15 days.

Grading of Clostridium difficile common antigen and toxin/toxin gene detection is based on a Positive / Negative result, no further statistical analysis is performed on the results beyond that described under “Suitability for grading(1) Famum NR. Acceptance sampling. In: Modern Statistical Quality Control and Improvement. Belmont, California.: Duxbury Press; 1994:305.

Posted in Clostridium difficile Results, critiques