Help Please log in to determine if you are eligible to purchase PT Programs. CYTOKINES - CTKN 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 Interferon (IFN)‑gamma 3 Two shipments per year Interleukin (IL)‑1 beta 3 IL‑2 3 IL‑6 3 IL‑8 3 IL‑10 3 Tumor necrosis factor (TNF)‑alpha 3 Vascular endothelial growth factor (VEGF) 3 Program Information Nine 2.0‑ to 3.0‑mL lyophilized serum specimens Shipping Schedule Shipment A: March 1 Shipment B: August 16 Guest Log in/Register