Performance evaluation of 14 specific proteins measurement checked by an External Quality Assessment Scheme

Aims of the study: To evaluate the state-of-the-art of 14 specific proteins measurement; to evaluate the laboratories’ performance and the degree of harmonization in reporting results of participants in the External Quality Assessment Program of the Centre of Biomedical Research (CRB). Methods: Overall and system-related inter-laboratory analytical variability (mean CVs%) and between-system differences (mean bias%) were evaluated from data of six EQA cycles 2013–2018. Moreover, we evaluated the analytical performance of participants as well as the units used to express proteins results. Results: Overall inter-laboratory variability ranged from 3.8% for haptoglobin (HPT) to 12.5% for α1-antitrypsin (AAT) and decreased for IgA, α2-macroglobulin (A2M) and transferrin (TRF). Mean CVs% were generally higher for Siemens BN and Beckman Immage immunonephelometric systems, but <7.0% for all proteins. Mean bias > 7.0% was observed for BN (IgA, C4, AAT, transthyretin TTR), Siemens Vista (IgA, C4) and Immage (C4), whereas mean bias < −7.0% was found for Immage (AAT), Beckman AU (IgM) and Roche Cobas (C4, TTR, C-reactive protein). The laboratories’ performance within the limits ranged from 85.1% of albumin (ALB) to 97.2% of HPT. The census of units employed in 2018, demonstrated that ~ 70% of laboratories still express the results in mg/dL. Conclusions: Despite a reduction in inter-laboratory variability for some proteins, different analytical systems showed both proportional and constant bias between methods. Units used by participants have not been substantially changed and dL is still largely used. The CRB EQA Program, with its performance data sets, is a valuable resource for laboratories and IVD manufacturers and support the goals of harmonization.