Unlike the causes of increases in other white blood cells, increases in monocytes often seem less specific and often of less concern, as is evident in this case. However, monocytosis should not be ruled out as a benign finding.
Two broad categories exist for causing monocytosis: reactive and clonal.
Reactive refers to the fact that an infection or other non-malignant trigger is causing an increase in monocytes. Clonal refers to an unchecked proliferation of the monocyte cell line due to a malignant condition.
In this case, it was clearly reactive due to the resolution of the monocytosis and the apparent respiratory infection. However, you should be aware that many other causes can be included in these categories.
