Mean platelet volume may not be a marker for disease activity in children with systemic lupus erythematosus

Sir, We read with great interest the prospective study of Talat et al. investigating the relationship between mean platelet volume (MPV) values and disease activity in children with systemic Lupus erythematosus (SLE). Researchers have suggested that MPV was a simple method that could be used to measure disease activity in children with SLE. We think that there are other factors that may have negatively affected the results of this study. At present, although the MPV value can be obtained in an easy, rapid, and inexpensive manner as part of a complete blood count, its measurement is still not standardized. Since its measurement is still not standardized, it is recommended that MPV value should not be used for purposes such as diagnosis or prognosis in acquired diseases. Anticoagulants used in complete blood count affect MPV values at different levels. The contact of the platelets taken from the patient with etylenediaminetetraacetic acid (EDTA), which is the most widely used anticoagulant in the whole blood tube, causes them to swell and increase in diameter. MPV values can increase up to 30% in the first five minutes and up to 40-45% in the first two hours, and although the majority of the change occurs in the first two hours, it can be extended to many more hours. In studies evaluating the ultrastructures of platelets by electron microscopic analysis, this chemical exposure to EDTA is associated with platelet swelling and increases in diameter. Lance et al. reported that the optimal measurement time for MPV should be 60minutes or 120minutes after blood collection, respectively, depending on whether citrate or EDTA is used as the anticoagulant. Various studies have reported that when using EDTA as an anticoagulant, MPV values might be deviated by 2-50% depending upon the measurement time. In the study of Talat et al., it was not stated which anticoagulant was used in the measurement of complete blood count and how long after blood was drawn that MPV measurements were performed. These are among the major factors that disrupt MPV standardization, and this made the data of the study on MPV unreliable. In addition, the MPV mean values were found to be 9.6 fL in the patient group with SLE, 9.1 fL in the healthy control group, 9.6 fL in the active stage patients and 8.5 fL in the patients with the remission stage. In the study, although the characteristics of the patient group and the healthy control group were not exactly matched (borderline agreement in terms of age and gender, significant difference in terms of weight), the statistical difference between the two groups was especially emphasized by the researchers. On the contrary, there is a need to explain why the MPV mean value in patients in the remission group is significantly lower than in the healthy control group. Obviously, while there are so many variables that affect MPV values, it may not be realistic to attribute any meaning to the MPV difference between the patient and control group. As a result, MPV values may not be useful in measuring disease activity in children with SLE.