Chapter 3 · External quality assessment

External quality assessment (EQA) provides an independent check on the accuracy of the laboratory’s results. The laboratory receives unknown samples, analyses them, and submits results to the scheme organiser. Results are compared against peer laboratories or a target value. Poor EQA performance must be investigated as a nonconformity. ISO 15189 requires EQA participation for all examinations where a scheme is available.

Chapter 3 · Practical example

EQA failure — investigating before the next cycle

A poor EQA result is a quality event. It must be investigated and corrected in the current cycle — not noted and waited out until the next cycle improves.

▲ The situation

The laboratory receives its quarterly EQA report. The PT/INR result shows a bias of plus 18% from the peer group mean — flagged as unacceptable. The quality manager is deciding how to respond.

Reference: ISO 15189:2022 Clause 7.3.8

✓
Good practice

The quality manager raises a formal nonconformity. Investigation: QC data from the same period is reviewed — a gradual upward drift in the high-level PT control is visible in the chart but did not trigger a Westgard rule. The analyser is recalibrated and reagent lot is reviewed. EQA samples are re-run with the recalibrated system. The next scheduled EQA cycle shows the bias resolved. The investigation and corrective action are documented.

✗
Poor practice

The quality manager records the EQA result as noted and waits for the next cycle, reasoning that internal QC was passing at the time. The next two EQA cycles show the same bias — 15% and 12%. Three consecutive poor results trigger a formal EQA provider review. What could have been resolved with a calibration check in month one is now a three-cycle finding on the laboratory’s accreditation record.

● What this means for your practice

EQA results are external feedback on accuracy. Poor results must be treated as quality events regardless of IQC status — because IQC measures precision, not accuracy against external references. Investigate every EQA failure in the same cycle it occurs.