Type of specimen for C. diff testing?

• A. Solid stool is required
• B. Urine sample
• C. Liquid stool is required
• D. Blood sample

Answer: (C)

For C. difficile testing, you need a stool specimen because the toxin-producing organism resides in the gut and the assays detect toxin or toxin genes in stool. Liquid (unformed) stool is preferred because it provides enough material and toxin for reliable detection and is easier to process, minimizing issues that can affect the test. Urine or blood do not contain the organism or its toxin in a form that these tests use, and formed solid stool can be harder to homogenize and may yield less reliable results. So, liquid stool is the best-suited specimen for this test.