Diurnal variation of circulating myeloperoxidase levels in patients with ST-segment elevation myocardial infarction

Myeloperoxidase (MPO) is a marker of inflammation that has been suggested to have prognostic role in patients with acute coronary syndrome. We sought to investigate whether day-night variations occur in the concentration of circulating MPO in patients with ST-segment elevation myocardial infarction (STEMI), as this may have practical implications. We assessed 70 consecutive STEMI patients admitted to the Coronary Care Unit and 50 age- and gender-matched apparently healthy control subjects. Blood samples were drawn at 09:00 a.m. (light phase) and 02:00 a.m. (dark phase). MPO was measured using a commercially available ELISA. MPO levels showed no diurnal variations in control subjects. In STEMI group, however, MPO concentration (ng/mL) in the dark phase was significantly higher than that in the light phase (83.30±33.08 vs. 64.10±31.30, p<0.001). The study shows for the first time the existence of diurnal variations in MPO levels in STEMI patients, which indicates the need for standardizing the time of blood sampling for the assessment of this molecule.