Last Updated on December 23, 2025 by Melissa Lazaro

Why Updating PT Schemes for ISO/IEC 17043:2023 Is Critical Now

Most PT providers assume their schemes are fine because they’ve worked for years. And to be fair, under ISO/IEC 17043:2010, many of them were fine.

What’s changed is how accreditation bodies now evaluate schemes.

In my experience, assessors no longer look at PT schemes as static products. They look at them as living systems that must clearly demonstrate purpose, control, and credibility under ISO/IEC 17043:2023.

This matters because scheme-level gaps are some of the hardest to defend during audits. You can fix a missing procedure quickly. A poorly justified scheme design is a much tougher conversation.

This guide focuses on how to update existing PT schemes so they clearly meet 2023 expectations—without unnecessary redesign or disruption.

What Changed in PT Scheme Expectations Under ISO/IEC 17043:2023

The biggest shift isn’t about adding new steps. It’s about clarity and justification.

ISO/IEC 17043:2023 places stronger emphasis on showing:

• why a scheme exists,
• how it achieves its objectives,
• and how design decisions support valid performance evaluation.

Under the 2010 version, many schemes relied on precedent. “We’ve always done it this way” used to pass. It doesn’t anymore.

Here’s what I’ve noticed in audits. Legacy schemes that haven’t been reviewed since launch tend to raise questions—not because they’re wrong, but because the logic behind them isn’t clearly documented.

Pro tip:
If you can’t explain your scheme design in plain language to an auditor, that’s a signal something needs updating.

Reviewing PT Scheme Objectives & Scope for ISO/IEC 17043:2023 Compliance

Scheme updates should always start with objectives.

Under ISO/IEC 17043:2023, objectives must clearly state:

• what competence is being evaluated,
• for whom,
• and for what intended use.

Vague objectives like “to assess laboratory performance” no longer hold up well. Auditors want to see fitness-for-purpose.

Scope matters just as much. Participants, matrices, measurands, and test methods all need to align with the objective. When they don’t, auditors notice.

I’ve seen audits stall because a scheme’s scope quietly expanded over time without formal review.

This is important because scope creep can undermine the validity of performance evaluation.

Updating PT Scheme Design & Planning Documentation

Once objectives and scope are clear, scheme design documents need to reflect them consistently.

This includes:

• scheme plans or protocols,
• timelines,
• sample distribution logic,
• and evaluation criteria.

ISO/IEC 17043:2023 expects design decisions to be intentional, not inherited.

A common mistake is updating wording without reviewing whether the design still fits the stated objective. That’s how internal inconsistencies creep in.

Pro tip:
Auditors don’t expect perfect design. They expect clear reasoning—and evidence that someone actually reviewed it.

Sample Preparation, Homogeneity & Stability – Scheme-Level Updates

Sample preparation is one of the most scrutinized areas in PT scheme assessments.

Under the 2023 standard, homogeneity and stability studies must clearly support the scheme design—not just exist as standalone records.

I often see providers treat these studies as “done once, done forever.” That’s risky.

If sample types, preparation methods, or measurands change, the justification needs revisiting.

Common pitfall:
Using historical homogeneity data without confirming it still applies to the current scheme round.

What works well:
Short, scheme-specific explanations linking sample studies directly to performance evaluation confidence.

Statistical Design & Performance Evaluation Updates for ISO/IEC 17043:2023

Statistics don’t need to be complicated—but they do need to be justified.

ISO/IEC 17043:2023 expects PT providers to explain:

• why a statistical method was chosen,
• how it supports the scheme objective,
• and how results should be interpreted.

I’ve seen technically correct statistics questioned simply because no one documented the reasoning behind them.

Outliers are another area where expectations are clearer now. Decisions must be transparent and consistent.

Real-world lesson:
Auditors rarely challenge statistics when the logic is clearly explained. Silence is what raises flags.

Updating Participant Instructions & Communication

Participant instructions often lag behind scheme updates.

Under ISO/IEC 17043:2023, instructions must clearly tell participants:

• what to do,
• how results will be evaluated,
• and what performance outcomes mean.

Overly technical instructions confuse participants and invite audit questions.

Pro tip:
If a competent lab manager needs to reread your instructions three times, they’re too complex.

Clear communication protects both scheme credibility and audit outcomes.

PT Scheme Reporting Updates – Meeting ISO/IEC 17043:2023 Expectations

Reports are where all scheme elements come together.

ISO/IEC 17043:2023 expects reports to clearly link:

• scheme objectives,
• evaluation criteria,
• statistical methods,
• and performance conclusions.

One of the most common findings I see is this: reports full of data, but short on explanation.

Participants should understand not just what their score was, but what it means.

Common mistake:
Assuming technical audiences don’t need interpretation. Auditors strongly disagree.

Risk & Impartiality Considerations at the PT Scheme Level

Risk and impartiality aren’t just system-level topics anymore. They apply directly to schemes.

Each scheme should consider risks such as:

• conflicts of interest in sample preparation or evaluation,
• single-person decision points,
• or reliance on subcontractors.

ISO/IEC 17043:2023 expects these risks to be identified and controlled at the scheme level.

Practical guidance:
If a scheme could be questioned for fairness or credibility, document how you prevent that—and monitor it.

Validating Updated PT Schemes Before Audit

Before rolling updated schemes into full operation, they should be reviewed and approved.

Validation doesn’t always mean pilot rounds. Sometimes it’s a structured internal review confirming:

• objectives still make sense,
• design aligns with execution,
• and reporting supports interpretation.

Auditors like to see evidence that updates weren’t rushed.

Pro tip:
A signed internal review record can be just as powerful as a pilot run when done properly.

FAQs – Updating PT Schemes for ISO/IEC 17043:2023 Compliance

Do all existing PT schemes need to be redesigned?
No. Many only need clarification and justification, not full redesign.

How detailed should scheme justifications be?
Detailed enough that an auditor can follow the logic without asking follow-up questions.

Will auditors review individual schemes during transition audits?
Yes. Expect sampling—especially of higher-risk or complex schemes.

Conclusion – Updating PT Schemes the Smart Way for ISO/IEC 17043:2023

Updating PT schemes for ISO/IEC 17043:2023 isn’t about starting over. It’s about making your existing schemes defensible, transparent, and aligned with current expectations.

From what I’ve seen in real audits, providers who proactively update schemes face fewer findings and far smoother assessments.

The key is timing. Review and update now—before an assessor forces the conversation.