A laboratory performs testing on an analyte with multiple methods. The laboratory ordered duplicate proficiency testing kits for that analyte. The proficiency testing provider refused to send two kits, but did send a kit for the primary test method. What is the most likely explanation for the proficiency testing provider's refusal to send two kits? Please select the single best answer Insufficient stock of kits Secondary method requires large volume of sample that is not available Test method not eligible for split sample testing Not permitted by regulatory agencies