Currently available computer-aided diagnosis (CAD) systems for the detection of anti-nuclear antibodies (ANA) by indirect immunofluorescence (IIF) assay enable a standardized measurement of system-specific fluorescent intensity (FI) measures. We aimed to evaluate an internal quality control (iQC) program that controls the total ANA IIF process in routine practice.
In addition to the kit iQC materials, supplemental quality indicators were integrated in a total quality assurance (QA) program: patient-derived iQC’s samples (negative, 1/160 fine speckled and 1/160 homogeneous), median sample FI per run and percentage of ANA IIF positive samples per run. Analytical rejection criteria were based on the imprecision of the positivity index (PI) measure of the Zenit PRO system (Menarini). Clinical rejection criteria were based on changes in FI that correspond to a change in ANA IIF titer of ≥2. To evaluate the QA program, different artificial errors were introduced during the ANA IIF process. After every run, quality indicators were evaluated and compared to the pre-set target values.
Rescanning the ANA IIF slides five times, using an old conjugate and a needle obstruction resulted in analytically and even clinically relevant errors in ANA IIF results. All errors were correctly detected by the different defined quality indicators. Traditional Westgard rules, including analytically (and clinically) defined rejection limits were useful in monitoring quality indicators.
The integration of a total process iQC program in CAD systems, based on the specific FI measurands and performance criteria of the system, adds value to QA.
We gratefully acknowledge lab technicians of OLV Hospital Aalst for their practical support and the colleagues of ASZ Aalst for the preliminary testing of the ANA IIF samples on their Zenit PRO instrument.
Research funding: None declared.
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Competing interests: Heidi de Baere, Daria Franceschi and Emiliano Tosi are employees of A. Menarini Diagnostics; Marco Meoni is an employee of Visia Lab Srl. All other authors state no conflict of interest.
Ethical approval: The study was performed according to the Declaration of Helsinki and approved by the local ethical committee of OLV Hospital Aalst (study registration number B126201942365).
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