Decision rules under ISO/IEC 17025:2017: guard banding moves mainstream

The 2017 revision of ISO/IEC 17025 made decision rules explicit: whenever a laboratory states conformity, the rule that accounts for measurement uncertainty must be documented and agreed with the customer.

ILAC-G8:09/2019 gives the practical menu — simple acceptance, guarded acceptance with the acceptance limit pulled in by the expanded uncertainty, and risk-calculated approaches per JCGM 106. Assessor findings on missing or undeclared decision rules remain among the most common 17025 nonconformities worldwide.

A workable starting point for most laboratories: declare guarded acceptance (w = U) for compliance statements, keep simple acceptance only where a documented risk analysis supports it, and put the rule text on the certificate.