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Lake Balance Calibration Solutions

Guide for calibration labs

ISO/IEC 17025 proficiency testing requirements

Proficiency testing is how an accredited calibration lab shows, with outside evidence, that its results and uncertainties hold up. Here's what the standard asks for, how accreditation bodies turn it into a schedule, and how to plan PT across your scope.

What clause 7.7.2 says

ISO/IEC 17025:2017 clause 7.7 covers ensuring the validity of results. Clause 7.7.1 covers internal monitoring such as check standards, replicate calibrations, and intermediate checks. Clause 7.7.2 adds external monitoring: the laboratory must monitor its performance by comparison with the results of other laboratories, where available and appropriate. That monitoring must be planned and reviewed, and it includes participation in proficiency testing, other interlaboratory comparisons, or both.

Clause 7.7.3 then requires you to analyze the data from these activities and use it to control and, where applicable, improve your lab's activities. If results fall outside pre-defined criteria, you take action to stop incorrect results being reported.

How accreditation bodies set PT frequency

The standard doesn't set a frequency. Accreditation bodies do, following ILAC policy, and the rules differ. Published policies we've seen follow a similar pattern:

  • At least one PT or ILC activity every year, with some bodies requiring more for larger scopes.
  • Coverage of every major area or sub-discipline on your scope within a four-year cycle.
  • A documented PT plan covering the current year and the next several years.
  • For initial accreditation, PT participation in at least part of the proposed scope, often within the previous 12 months.

Requirements change. Check the current PT policy from your accreditation body (for example A2LA, ANAB, PJLA, or IAS) before you finalize your plan.

Building a four-year PT plan

  1. List the areas on your scope. Group them the way your accreditation body does: for example mass, scales and balances, volume, dimensional, thermodynamic, pressure, and electrical.
  2. Rank by risk. Put high-volume work, areas with tight uncertainties, new technicians, new standards, and any past unsatisfactory result early in the cycle.
  3. Pick representative programs. One PT can represent similar items and ranges. For example, a 200 g analytical balance PT for analytical balance calibration.
  4. Include more than one participant where it matters. Adding technicians to the same kit shows consistency across your staff at a fraction of the cost of a second program.
  5. Review every year. Update the plan after scope changes, staff changes, and each PT result.

Choosing a PT provider

Accreditation bodies generally prefer PT from a provider accredited to ISO/IEC 17043, and you should confirm the provider's scope covers the scheme you're buying. Also look at whether the artifact is a realistic match for your customer work, how results are scored, and how quickly you get a report you can hand an assessor.

Lake Balance is accredited by PJLA to ISO/IEC 17043:2023 (certificate L24-898). The certificate and scope are on our accreditation page. Results are scored with En numbers.

Frequently asked questions

Is proficiency testing mandatory for ISO/IEC 17025 accreditation?

ISO/IEC 17025:2017 requires comparison with other laboratories where available and appropriate, and accreditation bodies turn that into a firm requirement. In practice, an accredited calibration lab is expected to take part in PT on a defined schedule and to keep a PT plan covering its scope.

How often does a calibration lab need to do proficiency testing?

It depends on your accreditation body. A common pattern is at least one PT activity every year, with every major area of the scope covered within a four-year cycle. Some bodies require more activities per year for larger scopes. Always follow the current PT policy from your own accreditation body.

What is the difference between proficiency testing and an interlaboratory comparison?

An interlaboratory comparison (ILC) is any organized comparison of measurements on the same or similar items by two or more labs. Proficiency testing is an ILC run by a provider that evaluates each participant's performance against pre-set criteria, ideally a provider accredited to ISO/IEC 17043.

What should we do after an unsatisfactory PT result?

Treat it as nonconforming work. Investigate the root cause (reference standards, procedure, environment, calculation, or an underestimated uncertainty), take corrective action, check whether past customer results were affected, and document the result. Many accreditation bodies also expect to be notified.

Proficiency testing programs Mass & balance PT