Determination of the erythrocyte sedimentation rate using the hematocrit‐corrected aggregation index and mean corpuscular volume

BACKGROUND: Determination of the erythrocyte sedimentation rate (ESR) by measurement of erythrocyte aggregation is an alternative to the Westergren method and can be performed rapidly. However, its principle is opaque and the ESR values obtained can deviate from Westergren method values (WG ESR) due to hematocrit. Furthermore, WG ESR is affected by particle size, but no studies have examined the effect of individual mean corpuscular volumes (MCVs). METHODS: Simultaneous measurement of the erythrocyte aggregation index (AI) over a 5‐s interval and determination of the complete blood count in 80 μL blood from 203 patients were performed (hematocrit, 21.4%–52.3%; MCV, 62.7–114.1 fL). ESR values were calculated with the hematocrit‐corrected AI (HAI) for comparison with WG ESR. We improved the calculation formula by using MCV. RESULTS: The sedimentation velocity of a single erythrocyte in the samples agreed well with an exponential function of HAI. ESR values calculated using HAI showed excellent correlation with WG ESR (r = 0.899, p < 0.001; Bland–Altman analysis: bias 2.76, limits of agreement (LOA) −24.5 to 30.0), but the difference between the calculated ESR and WG ESR increased with decreasing MCV. Calculation of ESR considering both HAI and MCV eliminated the MCV‐dependent deviation and improved the correlation with WG ESR (r = 0.920, p < 0.001, bias −2.17, LOA −24.6 to 20.3). CONCLUSION: Calculation using HAI and MCV can rapidly provide ESR values that are highly correlated with WG ESR in clinical specimens over a wide range of hematocrit and MCV values.