Although there are no clear guidelines or a particular “threshold” for leucocytosis or HbS levels to induce crises, there is some suggestion that it is the best to avoid G-CSF in patients with HbS levels of more than 30% and to stop therapy if there is significant leukocytosis (>80 × 109/L) [17, 18]. This evidence concerns the gene CSF3 and Increased total leukocyte count.