EQAS & Proficiency Testing for NABL Labs in India

What is EQAS / proficiency testing?

External Quality Assessment (EQAS) — used interchangeably with proficiency testing (PT) — is an independent check on the accuracy of your laboratory's results. An external provider distributes blind samples of known or consensus value to many participating laboratories. Each lab tests the samples using its routine methods and reports results back. The provider then compares every lab's result against the assigned value and returns a performance report, usually as a Z-score or SDI.

EQAS is the external counterpart to your daily internal quality control (IQC). Where IQC and Westgard multi-rules tell you whether your instrument is stable from run to run, EQAS tells you whether it is correct compared with peer laboratories and reference methods. Both are mandatory pillars of a NABL / ISO 15189 quality system — neither replaces the other.

ISO 15189:2022 & NABL requirements

ISO 15189:2022 addresses external quality assessment under clause 7.3.7. The laboratory shall participate in an inter-laboratory comparison programme (such as an EQA or proficiency-testing scheme) appropriate to the examination and monitor the results, taking corrective action when predefined acceptance criteria are not met (clause 7.3.7.3). Where a suitable programme is not available, clause 7.3.7.4 requires the laboratory to use an alternative approach and to justify it.

For accreditation in India, NABL applies these ISO 15189 requirements through NABL 112 (specific criteria for medical laboratories) and its proficiency-testing policy. In practice the assessor expects:

• A documented PT plan that covers every test in the accredited scope across the accreditation cycle — not just a few flagship analytes.
• Participation in an ISO/IEC 17043-accredited PT provider wherever one exists for the test.
• Records of results, performance scores, and corrective action for any unsatisfactory outcome.
• A documented alternative assessment (e.g. inter-laboratory comparison) for tests with no available scheme.

NABL-accredited EQAS / PT providers in India

NABL accredits proficiency-testing providers to ISO/IEC 17043, and NABL is a signatory to the APAC mutual-recognition arrangement for this program. The authoritative, current list is NABL's Directory of Accredited PT Providers (NABL 700). Widely used schemes for medical laboratories include:

Provider names are given for orientation; always confirm current accreditation status and available parameters against NABL 700 and the provider's own catalogue before enrolling.

How to choose a scheme

Building a PT plan & frequency

NABL expects a written proficiency-testing plan, reviewed and updated, that demonstrates coverage of the whole scope over the accreditation cycle. ISO 15189 does not fix a single universal number of cycles; frequency is planned according to the test, its clinical risk, and the schemes available — many chemistry and haematology programmes run 3 to 12 cycles a year, while specialised schemes run fewer.

A defensible plan typically states, for each accredited test: the scheme/provider, the number of cycles per year, the acceptance criterion, and how gaps (uncovered tests) are handled by alternative assessment. Keeping this as a live grid — rather than a once-a-year document — makes assessment far smoother.

Interpreting your result: Z-score & SDI

Most schemes grade performance with a Z-score (or the equivalent SDI), calculated as the distance of your result from the assigned value in units of the scheme's standard deviation. Under ISO 13528:

Two acceptable-but-drifting results on the same side of the assigned value can matter as much as a single failure — a persistent bias is a real signal even before it breaches the limit. Track scores over time, not just cycle by cycle.

When no EQAS scheme exists: inter-laboratory comparison (ILC)

Not every test has a commercial PT scheme. ISO 15189:2022 clause 7.3.7.4 explicitly allows alternative approaches, provided they are documented and justified. Recognised options, evaluated with ISO 13528 statistics, include:

• Inter-laboratory comparison (ILC) — exchange a sample with at least two peer laboratories (preferably NABL-accredited for that test) and compare results against a robust consensus.
• Split-sample exchange with a reference or comparator laboratory.
• Analysis of certified reference materials (CRM) with known values.
• Re-testing retained samples or blind duplicates within the laboratory.

For a two-lab exchange the result is commonly judged against the analyte's total allowable error (TEa); for three or more labs a robust mean and Z-score (ISO 13528, with En numbers when measurement uncertainties are available) is used. Whatever the design, record why no scheme was available and review at least annually whether a proficiency scheme has since become available — migrating back to a formal scheme when one exists.

Handling an unacceptable result

An unsatisfactory PT/EQAS score is not a black mark — assessors want to see that you detected it and acted. A sound response records:

1. Immediate check — clerical/transcription error, wrong units, sample mix-up, or reconstitution error ruled out first.
2. Technical investigation — calibration status, reagent/lot, instrument maintenance, method bias, and IQC around the survey date.
3. Root cause & corrective action — a documented CAPA with the fix and a verification step.
4. Effectiveness check — confirmation that the next cycle (or a targeted re-test) returned to acceptable performance.

Repeated or uncorrected unsatisfactory performance for the same analyte is what actually threatens accreditation — a well-documented CAPA loop is what protects it.

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