Letter to the Editor Myeloperoxidase as a diagnostic and prognostic marker in cardiology: beware of pre-analytical factors that may influence results Dear Editor We read with great interest the article by Dr Pawlus et al. (2010) who studied, among other parameters, the diagnostic and prognostic value of serum myeloperoxi- dase (MPO) levels in patients with coronary artery dis- ease. They found significantly increased MPO levels in patients with unstable angina and myocardial infarction when compared to controls and patients with stable angina. In addition, they demonstrated a high diagnostic sensitivity of MPO in all study groups. Although these results seem of relevance to clinical laboratory practice, we would like to stress the impor- tance of pre-analytical factors, i.e. collection tube and sample handling, which may bias results (Schindhelm et al., 2009). A number of studies have demonstrated that MPO levels were significantly higher, when blood was collected in tubes with heparin as anticoagulant or in case tubes without anticoagulant (serum) were used (Chang et al., 2006; Scheffer et al., 2009). The higher lev- els of MPO in serum and heparin plasma when compared to EDTA plasma may be the result of poorly controllable ex vivo release because of the coagulation-induced activation of leukocytes or because of heparin-induced degranulation of leukocytes, respectively (Le´ culier et al., 1993; De Gaetano, Cerletti & Evangelista, 1999). Hence, EDTA tubes were suggested as the preferred collection tube type for MPO measurement, because this may best reflect MPO concentrations in circulation (Chang et al., 2006; Scheffer et al., 2009). The study by Pawlus et al. (2010) provides interesting insights in the role of MPO as a diagnostic and prognostic parameter and further adds to the growing body of evi- dence that MPO may be a valuable parameter in diagnos- tic and prognostic cardiology. However, standardization in sample handling and assay methods is still required (Schindhelm et al., 2009). R. K. Schindhelm*, L. P. van der Zwan † * Department of Clinical Chemistry, Isala Clinics, Zwolle, The Netherlands † Department of Clinical Chemistry, VU University Medical Center, Amsterdam, The Netherlands E-mail: roger@schindhelm.nl doi: 10.1111/j.1751-553X.2010.01281.x References Chang P.Y., Wu T.L., Hung C.C., Tsao K.C., Suna C.F., Wu L.L. & Wu J.T. (2006) Devel- opment of an ELISA for myeloperoxidase on microplate: normal reference values and effect of temperature on specimen prepara- tion. Clinica Chimica Acta, 373, 158–163. De Gaetano G., Cerletti C. & Evangelista V. (1999) Recent advances in platelet-polymor- phonuclear leukocyte interaction. Haemosta- sis, 29, 41–49. Le´culier C., Couprie N., Adeleine P., Leitienne P., Francina A. & Richard M. (1993) The effects of high molecular weight- and low molecular weight-heparins on superoxide ion production and degranulation by human polymorphonuclear leukocytes. Thrombosis Research, 69, 519–531. Pawlus J., Holub M., Ko _ 0 zuch M., Da˛ browska M. & Dobrzycki S. (2010) Serum myeloper- oxidase levels and platelet activation parame- ters as diagnostic and prognostic markers in the course of coronary disease. International Journal of Laboratory Hematology, 32, 320– 328. Scheffer P.G., Van der Zwan L.P., Schindhelm R.K., Vermue H.P. & Teerlink T. (2009) Mye- loperoxidase concentrations in EDTA-plasma of healthy subjects are discordant with con- centrations in heparin-plasma and serum. Clinical Biochemistry, 42, 1490–1492. Schindhelm R.K., Van der Zwan L.P., Teerlink T. & Scheffer P.G. (2009) Myeloperoxidase: a useful biomarker for cardiovascular disease risk stratification? Clinical Chemistry, 55, 1462–1470. LETTER TO THE EDITOR INTERNATIONAL JOURNAL OF LABORATORY HEMATOLOGY 332 Ó 2010 Blackwell Publishing Ltd, Int. Jnl. Lab. Hem. 2011, 33, 332 International Journal of Laboratory Hematology The Official journal of the International Society for Laboratory Hematology