Standards profile: ISO/IEC 17043 — who tests the testers

Proficiency testing only means something if the scheme itself is competent — the assigned value honest, the items stable and homogeneous, the statistics sound. ISO/IEC 17043 is the standard that disciplines the disciplinarians: competence requirements for PT providers, in the same 17000-family mold as 17025 itself.

The 2023 revision aligned the standard's structure with modern conformity-assessment practice and sharpened requirements around scheme design and the statistical backbone, which lives in ISO 13528: assigned values (from formulation, reference labs, or participant consensus, each with its own uncertainty), performance statistics, and the homogeneity and stability studies that keep an artifact comparison fair.

For a participating laboratory, the practical use of 17043 is procurement: accreditation of the PT provider against it is what makes an En score evidence rather than opinion. The earlier En-number article covers how to read the score; 17043 is why the score is worth reading.