Proficiency Testing/EQA / 2024 Surveys / Microbiology / Bacteriology Help Please log in to determine if you are eligible to purchase PT Programs. C DIFF, 2 CHALLENGE - CDF2 Analytes/procedures in bold type are regulated for proficiency testing by the Centers for Medicare & Medicaid Services (CMS). Analyte Challenges per Shipment Number of Shipments Clostridioides (Clostridium) difficile antigen/toxin 2 Two shipments per year Program Information Two 0.5‑mL lyophilized specimens, for use with rapid or molecular testing methods Shipping Schedule Shipment A: April 15 Shipment C: December 9 Guest Log in/Register