Discussion
To our knowledge, this is the first study comparing the ESR STAT PLUS centrifugation method with the Westergren method. The latter is the recommended standard testing method by the International Committee for Standardization in Haematology.[3] There are many factors that result in an increase in the ESR, including increasing age, female sex, amount of circulating fibrinogen levels,[5] and degree of anemia. Conversely, the ESR may be low with polycythemia, hypofibrinogenemia, or erythrocyte abnormalities, such as spherocytes or sickle cells.[2] In this head-to-head study, the preanalytic factors were identical because identical blood samples were analyzed in tandem. Therefore, the ESR differences reflect analytic differences between the methods.
The centrifugation method uses multiple optical readings of the erythrocyte-plasma interface to determine the ESR. In the general patient study, the centrifugation ESR exceeded the Westergren ESR by a small (95% confidence interval, 1.52-5.08 mm/h) but statistically significant amount in the lower range (0-20 mm/h), where most normal ranges fall ( Table 1 ). This difference in ESR was even greater in the sickle cell group (95% confidence interval, 6.95-11.07 mm/h), in which 97% of the samples tested demonstrated a higher centrifugation ESR than Westergren ESR. The discrepancy did not seem to correlate with the level of hemoglobin S in the sample. The sickle cell study showed that there are certain patient populations in which a systematic bias can occur between the Westergren method and the centrifugation method. It is unclear if this bias also occurs in other patient populations in which the ESR test may be ordered. Patients with sickle cell disease often demonstrate a low ESR owing to hindrance of rouleau formation by the sickled morphologic features.[6] However, the ESR may be an important test to identify subsets of patients with sickle cell disease at risk of bacterial infection.[7]
The ESR STAT PLUS centrifugation-based ESR has the potential benefit of requiring a smaller volume than other Westergren method ESRs and can produce a result in a shorter time. However, there are concerns about its correlation with the reference Westergren method, especially in the 0-20 mm/h range, where most normal ranges fall. In addition, this centrifugation method requires a minimum of 15 mixing intervals, followed by a 5-minute limit (maximum) before drawing into the capillary tube. If this process is not strictly followed, the process must be repeated with another capillary tube. Failure to do so can result in higher intra-assay variation. Because human error can occur in any busy hematology laboratory, it is critical that procedures be as straightforward as possible to achieve accurate ESR results.
We thank the hematology laboratory technologists at Children's Hospital of Philadelphia for help in conducting this study.
Reprint AddressAddress reprint requests to Dr Shelat: Hematology Laboratory, Children's Hospital of Philadelphia, Clinical Laboratories, 5 Main, 34th St and Civic Center Blvd, Philadelphia, PA 19104.
Am J Clin Pathol. 2008;130(1):127-130. © 2008 American Society for Clinical Pathology
Cite this: Differences in Erythrocyte Sedimentation Rates Using the Westergren Method and a Centrifugation Method - Medscape - Jul 01, 2008.
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