Proficiency Testing/EQA / Microbiology / Bacteriology Help Please log in to determine if you are eligible to purchase PT Programs. SHIGA TOXIN - ST 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 Shiga toxin 2 Two shipments per year Program Information Two 0.5‑mL liquid specimens For use with direct shiga toxin testing only; not compatible with culture methods, cytotoxicity assays, or PCR Not available to international customers due to United States export law restrictions Shipping Schedule Shipment A: February 13 Shipment B: July 31 Guest Log in/Register