Letter by Schindhelm regarding article, "High levels of systemic myeloperoxidase are associated with coronary plaque erosion in patients with acute coronary syndromes: a clinicopathological study".

Letter by Schindhelm Regarding Article, “High Levels of Systemic Myeloperoxidase Are Associated With Coronary Plaque Erosion in Patients With Acute Coronary Syndromes: A Clinicopathological Study” To the Editor: In their very elegant study, “High Levels of Systemic Myeloperoxidase Are Associated With Coronary Plaque Erosion in Patients With Acute Coronary Syndromes: A Clinicopathological Study,” Ferrante et al1 report significant differences in systemic serum myeloperoxidase (MPO) concentrations between patients with plaque rupture and patients with plaque erosion. The authors report “strikingly” higher levels of MPO in the latter group of patients. However, this difference between the 2 groups was tested with a Mann-Whitney U test. In Tables 1 and 2 of their article, it is clear that smokers are overrepresented in the group of patients with plaque erosion and that smokers have significantly higher serum MPO levels. Therefore, it seems more appropriate to test the differences in systemic MPO concentration between the 2 groups by multiple regression analyses to adjust for smoking status as a possible confounding variable.2 Furthermore, it would be of great value if the authors would comment on the issue of preanalytical factors affecting MPO levels. We and others have previously argued that EDTA collection tubes (ie, EDTA plasma) should be the preferred sample for the measurement of MPO concentration.3,4 Serum collection tubes, which were used in the study by Ferrante et al, might have influenced the presented results because of the uncontrollable ex vivo release of MPO from leukocytes during and after sample collection. Nevertheless, the study by Ferrante et al provides interesting insights in the role of MPO as an inflammatory biomarker in the pathophysiology of atherosclerosis, and warrants further research in the applicability of MPO as a prognostic marker in cardiology.5