A high monocyte count is called monocytosis and is defined as an absolute monocyte count above 10% or 800 per mm3. Monocytosis can be caused by a range of issues, including infections, inflammation, blood disorders, and other health issues. Some conditions that can cause monocytosis include endocarditis, tuberculosis, syphilis, collagen vascular disorders, sarcoidosis, protozoan or rickettsial infections, bone marrow recovery, hematologic disorders, and certain cancers. A high monocyte count can also be linked with some types of cancer, especially leukemia. However, a high monocyte count doesnt necessarily mean you have a serious medical condition, and doctors interpret monocyte levels in the context of other factors and tests. If you have monocytosis, your healthcare provider will take a close look at your overall health so they can identify and treat any underlying cause.