Abstract

Objective: External Quality Assessment (EQA) programs are critical for ensuring analytical accuracy, diagnostic reliability, and harmonized laboratory performance. Despite their importance, few EQA schemes are specifically tailored for Dried Blood Spot (DBS)-based newborn screening (NBS). Since 2009, the SIMMESN Society has coordinated EQA programs to support NBS laboratories across Italy and Europe, expanding these initiatives in response to the progressive enlargement of screening panels.

Materials and Methods: Between 2019 and 2025, SIMMESN managed five quantitative Quality Control (QC) and two Proficiency Testing (PT) schemes covering first- and second-tier NBS assays. Every year, twelve DBS samples per QC scheme were distributed, spanning normal to pathological concentration ranges. Performance was evaluated using consensus-based assigned values and statistical indicators (precision, linearity, and recovery) integrated into a global performance score. PT assessment focused on correct analyte identification, diagnostic interpretation, and the appropriateness of follow-up recommendations.

Results: During the study period, 396 QC samples were distributed to a participant base of 15 to 34 laboratories. Analytical performance was consistently satisfactory: mean intra- and inter-laboratory coefficients of variation remained generally below 12.1% and 14.8%, respectively. Robust linearity and recovery were observed, with median correlation coefficients between 0.978 and 0.998. The mean performance score was 8 for all analytes. PT results confirm high diagnostic competence, with most laboratories correctly identifying target disorders.

Conclusions: SIMMESN EQA programs provide a robust, evolving framework for continuous quality improvement in NBS. These schemes facilitate the harmonization of analytical performance and enhance diagnostic reliability amidst the challenges of expanded screening. Observed inter-year variability identifies specific analytical steps that require further training, underscoring the essential educational role of EQA within the NBS community.