Proficiency Testing (PT)
TestingAlso known as: PT, Interlaboratory Comparison, ILC, PT Scheme, Ring Trial
External evaluation where labs test unknown samples to demonstrate measurement accuracy.
What It Means
Proficiency testing is a formal quality assurance mechanism where an external provider sends identical reference samples to multiple laboratories. Each lab analyzes the samples independently, and results are compared against reference values and other participants using z-scores (a statistical measure of deviation). ISO 17025 clause 7.7 requires labs to participate in PT programs where available. For supplement testing, relevant PT programs include FAPAS (operated by Fera Science, covering food contaminants, nutrients, and mycotoxins) and LGC AXIO PHARMASSURE (pharmaceutical and supplement matrices). PT participation with consistently acceptable z-scores is the strongest publicly verifiable signal of analytical competence after accreditation itself.
What It Is Not
Proficiency testing is NOT the same as NIST's Dietary Supplement Quality Assurance Program (DSQAP). NIST describes DSQAP exercises as interlaboratory comparability tools for quality assurance, not proficiency tests with strict pass/fail evaluation under ISO 17043. Both are positive quality signals, but they serve different purposes and should be classified separately. PT is also not a one-time event — it is an ongoing commitment, typically with multiple rounds per year.
Evidence and References
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