Evaluation of a new soluble transferrin receptor assay and comparison to three measurement procedures

Background: Soluble transferrin receptor (sTfR) is a useful marker in the differentiation of anemia. Clinical utility is limited by lack of standardization between measurement procedures and interpretative recommendations. Our objective was to evaluate the analytical performance of a research sTfR immunoturbidimetric assay (Alinity c, Abbott Diagnostics) and compare it to three established measurement procedures. Methods: Assay imprecision was assessed with 7 panels across the analytical measuring interval. 159 patient samples were measured across four instrument systems (Alinity c [Abbott Diagnostics], Tina-quant c502 [Roche Diagnostics], Quantex Biokit [Werfen], and ACCESS [Beckman Coulter]). Ferritin was also measured to calculate an sTfR/Log Ferritin ratio. Sera from 100 reference individuals were assayed for sTfR and ferritin (Alinity) for reference interval (RI) verification (sTfR) or establishment (sTfR index). Results: Assay imprecision met defined goals. Method comparison between Alinity c and ACCESS sTfR assays showed good agreement (slope: 1.06, intercept: -0.12, r: 0.989). Comparisons across other assays demonstrated significant proportional bias with slopes ranging from 0.44 (Tina-quant c502, mean bias: -2.52 mg/L) to 1.24 (Quantex Biokit, mean bias: 0.60 mg/L). A proportional bias was observed between other instruments. While the sTfR RI was verified on the Alinity assay, agreement in interpretation (within vs outside RI) between Alinity and other platforms ranged from 74.2 to 80.5 %. Conclusion: We report the first characterization of the performance of a research sTfR immunoturbidimetric assay (Alinity c, Abbott Diagnostics). Our findings emphasize the lack of harmonization between measurement procedures and result interpretation for sTfR and sTfR index, necessitating standardization efforts and clinical studies.