Monocytes and neutrophils share a common precursor cell, the granulocyte lineage progenitor. Monocytes stay in the bloodstream for a short period of time, only 1-3 days, before they spill out of the blood vessels into the tissues and body cavities where they are transformed into macrophages. High monocytes indicate the presence of certain infections in the body, such as infectious mononucleosis, malaria or tuberculosis. In addition, certain hematologic disorders, such as monocytic leukemia, can also have high monocytes, as can lymphoma and myelodysplastic syndrome.