Comparison of Erythrocyte Sedimentation Rate Measurement by the Automated SEDIsystemTM and Conventional Westergren Method Using the Bland and Altman Statistical Method

OBJECTIVES: To compare the performance of SEDIsystem(TM), a fully automated analyzer for the measurement of the erythrocyte sedimentation rate (ESR), with the manual Westergren method. MATERIALS AND METHODS: Both methods were applied to 150 randomly selected subjects. The linear regression and Bland and Altman data analysis methods were used to measure the agreement between the automated and manual methods. RESULTS: The regression analysis showed a good correlation between the two methods (r=0.91). The Bland and Altman data analysis showed no systematic bias (95% confidence interval for mean difference); however, limits of agreement were between 11.52 and -37.88. This indicates that ESR values measured by the SEDIsystem may be 11.52 mm/h above or 37.88 mm/h below the reference method. A greater scatter of data was also observed with abnormally high (>25 mm/h) ESR results (mean of difference=-21.4 and limits of agreement=-45.2 and 2.26) compared with normal (<25 mm/h) readings (mean of difference=-3.9 and limits of agreement=-13.5 and 5.7). CONCLUSION: The Bland and Altman statistical analysis showed a wide degree of scatter between results obtained by the two ESR techniques that was not clearly demonstrated using the linear regression analysis. The automated system was found to underestimate ESR with the Bland and Altman statistical analysis, and therefore a correction factor is recommended.