A laboratory may say it participates in proficiency testing. That is useful information, but the statement needs context. What was tested? What did the evaluation show? How did the laboratory respond?
For readers in Ireland and elsewhere in Europe, the practical starting point is to treat proficiency testing as a piece of evidence with boundaries. Understanding those boundaries makes a technical claim easier to interpret without turning it into a blanket assurance.
What is proficiency testing?
Proficiency testing, often shortened to PT, evaluates performance against criteria established in advance through comparisons between laboratories. A provider commonly distributes test materials, collects results and evaluates them. Each distribution is called a round. The material, substances measured, concentration levels and evaluation rules define what that round can show. Eurachem’s guide to proficiency testing explains these principles.
Is participation the same as passing?
No. Participation describes taking part; satisfactory performance describes an evaluation outcome. A participation statement alone leaves the outcome unanswered. Ask which round and reported measurements the statement refers to, and whether the report actually assesses performance.
For numerical tests, evaluation may compare a result with an assigned value: the value attributed to the measured property of the test material. Its basis, uncertainty and the scoring approach matter. Schemes do not all use identical rules. Agreement with a peer consensus is not automatically proof of an error-free value; shared measurement problems remain possible. The Eurachem guide discusses assigned values and evaluation methods.
Does a good result cover every test?
Consider a hypothetical statement: “The laboratory performed satisfactorily for substance A in an oil sample.” That does not, by itself, answer whether it performs satisfactorily for substance B in a powder. Nor does it tell the reader what happened in an earlier or later round. These are separate questions, requiring their own evidence.
A helpful reading habit is to keep the claim as specific as its supporting report. “Satisfactory for these measurements in this round” communicates more clearly than an unexplained “passed laboratory testing”. For related context, see our explanations of laboratory methods and sample matrices and laboratory accreditation scope.
Are all interlaboratory comparisons graded?
No. NIST describes its Cannabis Laboratory Quality Assurance Program as a comparison programme intended to help laboratories demonstrate and improve measurement comparability or competence, without pass/fail grades. This distinction matters when interpreting a certificate of participation. See NIST’s programme explanation.
A historical example is its first exercise, reported in 2021, which examined cannabinoid measurements in two hemp oils. Participants were anonymised, and the emphasis was educational. The Exercise 1 report therefore illustrates why “participated in a comparison” cannot automatically become “received a passing grade”. This US example is neither a certification scheme for European products nor a statement of Irish or EU law.
What should happen after a poor result?
A poor result calls for investigation. It should neither be dismissed nor treated, on its own, as proof that every activity at the laboratory is unreliable.
Eurachem’s April 2025 participant checklist recommends reviewing the report promptly, checking that submitted results are represented correctly and considering the provider’s comments. Follow-up includes investigating poor performance, assessing whether customer results may have been affected, making relevant corrections and examining trends over time.
The same checklist emphasises practical details: suitable handling and storage, measurements under conditions close to routine testing unless instructed otherwise, and accurate reporting of units and results. This makes the response to a problem informative too. A useful explanation identifies what was examined, what changed and how the effectiveness of that change was checked.
What can you reasonably conclude?
Read a PT statement by asking four questions:
- Which provider, exercise and date does it identify?
- Which material and measurements does it cover?
- Does the report give a performance assessment or an educational comparison?
- What explanation accompanies any concerns or limitations?
Proficiency testing is not product safety certification. A comparison report about laboratory performance does not establish that a particular retail batch meets every relevant requirement. Questions about the sample representing that batch remain separate; our article on batch sampling and measurement uncertainty explores that distinction.
Sources
- Eurachem: Selection, Use and Interpretation of PT Schemes, third edition, 2021.
- Eurachem: Basic instructions for participants, April 2025.
- NIST: CannaQAP Exercise 1 Final Report, 2021.
- NIST: Laboratory quality assurance programme overview.
Educational information. Sources reviewed 19 October 2026.