External Quality Assurance (EQA)

Introduction & Context

  • Lecturer welcomes students back from the break and explains that this is the final screencast of the lecture series.

  • Focus: External Quality Assurance (EQA) within the laboratory quality management system.

Why EQA Is Needed

  • Internal Quality Control (IQC) only compares the laboratory’s current performance with its own historical data.

  • Laboratories also need to benchmark their results against:

    • Other laboratories using the same analyzer, reagent, and analytical principle.

    • Reference laboratories.

  • Primary objectives of EQA:

    • Detect and quantify systematic error (bias).

    • Monitor and maintain long-term accuracy of analytical methods.

    • Provide data for lab accreditation and continuous improvement.

EQA in the ISO 15189 Quality Management Framework

  • ISO 15189 quality policy has two complementary systems:

    1. Internal QC (IQC): Daily monitoring of precision and accuracy.

    2. External Quality Assurance (EQA): Periodic comparison among laboratories.

  • EQA frequency: Fortnightly or monthly (not daily).

Types of EQA Schemes

  • 1. Proficiency Testing (PT)

    • External provider dispatches unknown samples from a common simulated-patient pool.

    • Participating labs analyze samples, submit results, receive comparative report.

    • Most Australian pathology laboratories are enrolled in RCPA QAP (Royal College of Pathologists of Australasia Quality Assurance Programs).

  • 2. Rechecking / Retesting

    • Previously read slides or samples are re-evaluated by a reference lab.

    • Enables inter-laboratory comparison for difficult-to-standardize assays.

  • 3. Site Visits & Sample Exchange

    • Applied when PT or retesting is impractical.

    • Laboratories may exchange specialized samples among themselves for cross-checking.

Mandatory & Practical Importance of EQA

  • Regulatory requirement for laboratory accreditation in Australia and globally.

  • Supplies actionable information:

    • Highlights abnormal results or trends.

    • Indicates problems with kits, reagents, instruments, or staff performance.

    • Guides staff training and process improvement.

Anatomy of an EQA Report (Vitamin D3 Example)

  • Report displays data in multiple visual formats:

    • Histograms – distribution of participant results.

    • Yuden (Youden) Plots – comparison of low vs. high concentration specimens.

    • Levi-Jennings (LJ) Charts – longitudinal performance.

    • Linearity Plots – response across concentration range.

  • White zones on plots = allowable performance specification (analogous to \pm 2SD in IQC).

  • Lab’s own results marked by:

    • Red triangles (histograms).

    • Crosses (Yuden plots).

Reading a Yuden Plot

  • Graph each cycle’s Low-control result (x-axis) vs High-control result (y-axis).

  • Interpretation:

    • If the cross sits inside the central square, both results meet acceptance criteria.

  • Peer Review Box

    • Inner rectangle within the Yuden plot.

    • Limits derived from peer-group performance rather than target values.

    • Allows comparison with labs using identical analytical principle, instrument, and reagent.

  • Example given: Vitamin D measured by Luminescence Immunoassay (LIA) on DiaSorin Liaison using DiaSorin reagents.

Other Display Formats

  • Levi-Jennings Style

    • Plots results over time against control limits.

  • Linearity Style

    • Evaluates analytical linearity across multiple concentration levels.

  • Result Summary Table

    • Tabulates numeric result, target, deviation, and performance verdict.

RCPA QAP Report – 2020 Makeover

  • New design introduced in 2020 (example shown for Total Bilirubin).

  • Core layout retained; visuals refreshed for clarity and aesthetics.

Big-Picture Take-aways

  • EQA complements IQC to ensure comprehensive quality management of the analytical phase.

  • Detects systematic errors, biases, reagent/kit issues, instrument drift, and operator problems.

  • Mandatory for accreditation and integral to continuous improvement cycles.

Analytical Phase Error Sources (Recap)

  • Lecturer presents flow diagram of total testing process.

  • Analytical-phase errors include:

    • Instrument malfunction

    • Reagent deterioration

    • Calibration errors

    • Operator mistakes

    • Environmental factors

  • Quality control (IQC + EQA) is the primary defense against these errors.

Closing & Next Steps

  • Additional slides include:

    • Summary bullets of key QC principles (not detailed in transcript).

    • Case studies on troubleshooting QC failures (to be discussed live via Collaborate Ultra).

  • Students encouraged to review cases before live session.

  • Lecturer signs off with wishes for a great week.