Nonequivalence of erythrocyte sedimentation rate assessed in whole blood anticoagulated with K2EDTA or sodium citrate

Background: According to the International Council for Standardization in Hematology (ICSH), the Westergren method is the reference technique for measuring erythrocyte sedimentation rate (ESR). Although this assay has been originally validated on whole blood anticoagulated with sodium citrate, the use of whole blood anticoagulated with dipotassium ethylenediaminetetraacetic acid (K2EDTA) is commonplace and acknowledged by ICSH. This study was hence planned to define how ESR values compare between these two sample matrices. Methods: A total number of 148 consecutive paired blood samples collected either in 3.5 mL, 3.2% trisodium citrate or 3.0 mL, 5.4 mg K2EDTA were randomly selected from all routine samples conveyed on a working day and assessed with the fully automated analyzer TEST 1. Results: The median [and interquartile range (IQR)] ESR value was more than double in K2EDTA (36 mm/h; IQR, 56 mm/h) than in citrate tubes (17 mm/h; IQR, 41 mm/h; P<0.001). The percentage of samples with ESR >20 mm/h was significantly higher in K2EDTA than in sodium citrate (66% vs. 47%; P=0.001). Conclusions: Although both K2EDTA and citrate tubes can be used for measuring ESR, results are not interchangeable and specific reference ranges shall be implemented.