How often should a lab participate in PT?
How often should a lab participate in PT?
For many labs, the answer seems straightforward: once a year, or whenever accreditation requires it. Participation often becomes part of the annual quality calendar. However, PT serves a broader purpose than simply fulfilling a periodic requirement. When planned thoughtfully, it helps labs monitor analytical performance, evaluate competence, and maintain confidence in the results they report. Guidance from ISO/IEC 17025:2017, NABL 163, and international discussions on PT participation encourage labs to look beyond fixed schedules and consider a risk-based approach to participation. When labs review PT participation from a practical perspective, following considerations usually shape the decision: Compliance, control, competence, cost, and the level of risk associated with the testing activity.
Compliance: Meeting Accreditation Expectations
Participation in PT is an important element in demonstrating competence under ISO/IEC 17025:2017. Clause 7.7: Ensuring the validity of results requires labs to monitor the reliability of their results through activities such as proficiency testing, interlaboratory comparisons, or other appropriate quality control measures.
Similarly, NABL 163 recommends that labs participate in PT programs relevant to their accredited scope wherever such programs are available.
The expectation, however, is not participation merely for documentation. Labs are expected to show that their PT participation is planned, relevant to the scope of testing, and useful in monitoring performance.
Control: Monitoring Analytical Performance
From a lab’s operational perspective, PT also provides an external reference point for evaluating analytical performance.
- Compare their results with peer labs
- Observe trends in their own performance
- Detect analytical issues early
- Review the consistency of testing methods.
When PT participation reflects the lab’s routine testing activity, it becomes an effective way to maintain control over testing performance.
Competence: Supporting Analysts and Methods
PT participation also plays a role in evaluating analyst competence and method performance.
Additional participation may be useful when:
- New analysts begin performing a test
- A method is newly implemented or modified
- Equipment or instrumentation has changed
- Previous PT performance requires closer monitoring.
In such situations, PT provides reassurance that both the method and the analyst are capable of producing reliable results under routine testing conditions
Ensuring PT Participation Represents the Laboratory Scope
Another important aspect of PT planning is ensuring that participation reflects the scope of the lab. Rather than selecting PT rounds randomly, labs may plan participation so that key parameters, matrices, and testing areas within the scope are represented over time. This approach provides a clearer and meaningful view of laboratory competence.
A Risk-Based Approach to Participation
International discussions on PT increasingly support risk-based participation planning. Factors that labs may consider include:
- How frequently a test is performed
- The regulatory or safety impact of the parameter
- Experience and competence of analysts
- Complexity and stability of the method
- Previous PT performance trends.
Cost: Making Participation Meaningful
Cost is naturally one of the considerations when labs plan PT participation. However, when participation is aligned with testing frequency, parameter risk, and performance monitoring needs, labs often find that PT becomes more purposeful.
Instead of participating in multiple unrelated schemes, labs can focus on programs that best represent their testing scope and quality objectives.
Supporting Labs through Proficiency Testing
At Envirocare Labs Proficiency Testing, our objective is not only to conduct PT programs but also to support labs in planning participation in a way that strengthens their quality systems.
If your laboratory is reviewing its PT participation plan or exploring PT programs relevant to its testing scope, our team would be happy to guide you.