ISO 15189, CAP or CLIA: Does Accreditation Improve QC?

ISO 15189 and CLIA laboratories compared: 29 % vs 44 % out of control daily, more than 15 % of ISO laboratories override failed QC

Many laboratories in Central Asia and the Caucasus are preparing for ISO 15189 or CAP accreditation, often expecting that the process itself will raise the quality of their results. The 2025 Great Global QC Survey by Westgard QC allows a reality check: it compares the QC practice of ISO 15189 laboratories with that of US laboratories working under CLIA.

The short answer: accredited laboratories do better on some points — but accreditation does not decide how good internal QC is. The laboratory does.

Three frameworks, one goal

The three frameworks differ in origin and in how they treat QC:

	ISO 15189:2022	CAP	CLIA
What it is	International standard for medical laboratories	Accreditation programme of the College of American Pathologists	US federal regulation for clinical laboratories
Who assesses	National accreditation bodies	Peer inspectors using CAP checklists	US authorities or approved accreditors
Internal QC	QC procedure designed for the intended quality; results reviewed	Detailed checklist requirements per discipline	Defined minimum, e.g. two levels of control per day for most quantitative tests
External quality assessment	Required for every examination	CAP proficiency testing; outside the US and Canada at least 6 months before accreditation	Proficiency testing for regulated analytes

What the survey found

Comparing ISO 15189 laboratories with CLIA laboratories, the survey reports:

out of control daily or several times a day: 29 % of ISO laboratories vs 44 % of CLIA laboratories;
Westgard multirules on all tests: 67 % vs 59 %;
QC frequency: CLIA laboratories mostly run QC once a day — the legal minimum becomes the maximum — while ISO laboratories spread over one, two or three times a day;
overriding failed QC: more than 15 % of ISO laboratories vs 6 % of CLIA laboratories;
no measurement uncertainty calculated: 11 % of ISO laboratories vs 34 % of CLIA laboratories — ISO 15189 requires it, CLIA does not.

Why accreditation alone is not enough

Standards require that QC exists, is planned for the intended quality and is reviewed. They do not prescribe which rule to use for which test. The survey author concludes that neither framework gives distinctive, practical guidance on QC design — so two accredited laboratories can run very different QC.

The override figure shows the risk: an accredited laboratory under time pressure may release results from failed runs more often than one under strict minimum rules. Inspectors know this and look at override logs, corrective actions and how QC limits were set.

What to fix before applying

Whether the target is ISO 15189 or CAP, these points are worth reviewing before the self-inspection:

control limits from your own mean and SD, recalculated at each lot change;
rules chosen per test, ideally from a sigma metric;
a written procedure for failed controls: troubleshooting before repeating;
an override log with reason, person and patient impact;
measurement uncertainty for every quantitative test;
an EQA programme for every examination, with documented review of each result.

The regional picture

In the survey, 76 % of responding European laboratories were ISO 15189-accredited and more than 60 % of Asian ones. In the Middle East, CAP was the most common framework (43 %), followed by ISO 15189 (35 %). For laboratories in our region, both routes are open — the choice often depends on clinical-trial ambitions, international patients and what local regulators recognise.

KombiMED is an official CAP distributor and helps laboratories on either route: the free CAP readiness assessment, an overview of the CAP accreditation process and the EQA planning guide.

Frequently asked questions

Does ISO 15189 accreditation improve internal QC?

It helps but does not guarantee it. In the 2025 Great Global QC Survey, 29 % of ISO 15189 laboratories were out of control every day, against 44 % of CLIA laboratories, yet more ISO laboratories overrode failed QC runs.

What is the difference between CAP and ISO 15189?

ISO 15189 is an international standard assessed by national accreditation bodies; CAP is the accreditation programme of the College of American Pathologists with peer inspections and detailed checklists. Laboratories outside the US and Canada must take part in CAP proficiency testing for at least six months before CAP accreditation.

What should we prepare first for accreditation?

Review the QC plan (limits, rules, handling of failures, override log), make sure measurement uncertainty is calculated and enrol in external quality assessment for every examination.

Sources

Survey figures: 2025 Great Global QC Survey: ISO and CLIA labs ↗ — Westgard QC; 2025 Great Global QC Survey: Europe ↗ — Westgard QC; 2025 Great Global QC Survey: Asia ↗ — Westgard QC; 2025 Great Global QC Survey: Middle East ↗ — Westgard QC. Standard: ISO 15189:2022 ↗ — ISO.