Abstract
Dear Editor,
We read with great interest the retrospective study of Duan et al examining the contribution of various parameters to the development of venous thromboembolism (VTE) in patients with critically ill coronavirus disease (COVID-19). 1 Researchers reported that mean platelet volume (MPV) values were found to be significantly higher in patients with COVID-19 who developed VTE compared to those without VTE, and they suggested that high MPV values could be a novel indicator for the risk of VTE. We would like to emphasize the existence of some factors that may have adversely affected the MPV results of this study.
In this study, Duan et al suggested that systemic inflammation increases the risk of VTE and therefore the hyperinflammatory response caused by COVID-19 infection is responsible for the increased risk of VTE in these cases. 1 Bath and Butterworth concluded that MPV values may be a surrogate marker for platelet inflammation based on early clinical studies. 2 However, on the other hand, MPV values sometimes have increased, and sometimes decreased also, even in studies performed in different inflammatory diseases published by similar researchers.3,4 The most likely reason for the conflicting results is the non-standardization of the MPV measurement methodology, and/or the retrospective nature of the studies. MPV measurement has not been standardized to date, and therefore, the use of MPV values for purposes such as diagnosing or determining prognosis, especially in acquired diseases, is strongly discouraged. 5 The main factors that negatively affect the standardization of MPV measurement are how long the MPV measurement is made after the blood draw, which anticoagulant is in the blood tubes, and which blood analyzers are used for the measurement.6–8 The most commonly used anticoagulant in blood tubes is ethylenediaminetetraacetic acid (EDTA), and contact with EDTA in the blood tube causes rapid swelling and enlargement of platelets and the development of pseudopods. 6 It has been reported that this rapid increase in diameter in platelets in the presence of EDTA can reach up to 30% in the first 5 minutes and up to 40% to 45% in the first 2 hours. 6 In various studies using EDTA in blood count measurement, anticoagulant-related deviation in MPV values has been reported between 2% and 50%.6,7 Other anticoagulants may also cause deviations in MPV values. Lance et al found that measurement of MPV should be made 1 or 2 hours after blood collection according to the use of sodium citrate or dipotassium EDTA as anticoagulants. 8 The use of different blood analyzers also causes deviations in MPV values and this deviation can reach up to 40%. 7 The data of this study were obtained retrospectively from the medical records of the patients at the time of admission to the hospital, and no methodological description of how MPV measurements were performed was made in this research article. This situation significantly affected negatively the reliability of the MPV data of the study. In addition, the retrospective nature of the study prevented preanalytical and analytical errors that adversely affected laboratory data, which is unacceptable especially for MPV measurements. Moreover, the absence of a healthy control group in the comparison of the MPV data of the patients also led to the inability to understand whether the MPV data of the patients were indeed pathologically increased.
As a result, MPV values may not be an indicator that can be used to determine the risk of VTE in COVID-19 patients.