Analytical Agreement Between the Vision C Automated ESR Analyzer and the Manual Westergren Reference Method: A Prospective Method Comparison Study

Background/Objectives: The erythrocyte sedimentation rate (ESR) is a widely used biomarker of systemic inflammation, with established roles in rheumatologic, infectious, and malignant disease. The Westergren method remains the reference procedure, but automated analyzers are increasingly used clinically, and methodological differences may introduce systematic bias. This study evaluated analytical agreement between the Vision C automated ESR analyzer (EDTA) and the Westergren reference (sodium citrate). Methods: This prospective, single-center study followed CLSI EP09-ED3. A total of 228 consecutive adult patients were enrolled. Agreement was assessed by Bland–Altman analysis, Passing–Bablok regression, and Pearson correlation, with subgroup analyses (<40, 40–80, >80 mm/h) and against RCPA allowable total error (TEa) specifications. Results: Bland–Altman analysis showed a significant mean bias of −3.30 mm/h (95% CI: −4.25 to −2.35), with increasing dispersion at higher ESR values indicating heteroscedasticity; regression-based limits of agreement therefore widened progressively with ESR magnitude. Passing–Bablok regression showed no proportional bias but a significant constant bias; subgroup regression was not performed due to truncated ranges. Correlation was strong overall (r = 0.961, p < 0.001) and declined across subgroups (r = 0.821, 0.740, 0.687), consistent with range restriction rather than reduced agreement. The analyzer met RCPA TEa criteria across both ranges (≤20 mm/h: bias −2.55 mm/h within ±6.0 mm/h; >20 mm/h: percentage bias −10.49% within ±30%), including the high-ESR subgroup (approximately 6–9%). Conclusions: The Vision C analyzer showed a significant, level-dependent negative bias versus Westergren, widening at higher ESRs; strong correlation and RCPA TEa compliance across the full range, including the high subgroup, support its suitability for routine use. Wide regression-based limits and the limited high subgroup sample size (n = 20) warrant caution and further study but do not support routine manual confirmation, since predefined acceptance criteria are met. Method-specific reporting and consistent instrument use in follow-up are recommended.