Diurnal variations of serum GM-CSF levels

We aimed to investigate the daily variations of serum granulocyte-macrophage colony-stimulating factor (GM-CSF) levels and to correlate them with peripheral blood cells counts. Venous blood samples from eleven healthy volunteers were taken four times a day, being at 08:00, 14:00, 20:00 and 02:00h and serum GM-CSF levels measured by ELISA. We could not find a significant overall difference among GM-CSF levels at four different times of the day using the Friedman test. On the other hand, serum GM-CSF levels at night (20:00h) were found to be significantly increased when compared to the morning levels (08:00h) using the Wilcoxon test (P=0. 022). The levels of lymphocytes and white blood cells (WBCs) at 20:00h were also higher than the morning levels (08:00h) as expected. While there was a strong relationship between the morning levels of GM-CSF (08:00h) and all measurements of peripheral blood cells during the day, the levels of GM-CSF measured at 02:00, 14:00 and 20:00h were found to be significantly correlated with only the WBC levels. It was concluded that there may be a significant difference between morning and night levels of GM-CSF and morning levels of GM-CSF may be more important in the regulation of WBC counts during the day. These variations warrant further studies about diurnal rhythms of haematopoiesis chronotherapy with CSFs.