Study on long-term biological variability of erythrocyte sedimentation rate

The aim of the study was the estimation of long-term within-subject variability of ESR. ESR was measured in 52 healthy persons of both sexes, aged 20-50 years, twice a month during 6 consecutive months, after the method of Westergren. The within-run imprecision, expressed as cv was 13.2% (mean value, = 3.9 mm h−1) and 3.8% ($= 16.0 mm h−1) respectively. The analytical day-to-day imprecision, calculated by duplicate measurements during 23 consecutive days, was s=0.6 mm h−1. The medians from within-subject variances were 0.9 for men and 8.6 for women, respectively. The 90th percentiles were 11.3 for men and 40.6 for women, respectively. The critical differences based on the median value (dk50) were 3.1 mm h−1 (men) and 8.3 mm h−1 (women). The critical differences based on the 90th percentile (dk90) are 9.5 mm h−1 (men) and 17.7 mm h−1 (women).