Firstly, it may not be prudent to diagnose a monocytosis or monocytopenia based on a differential leukocyte count. At best, an increased monocyte % in a differential count may help to raise suspicion and lead to an "absolute" monocyte count, which is more reliable.
The normal range for monocytes in a differential count is 0-9%.
The normal reference range for an absolute monocyte count is
40 - 950/µL. A value >950/µL is called as Monocytosis.
Monocytosis is seen in some of the following disorders,
- recovery phase of many acute infections,
- chronic infectious disorders (tuberculosis),
- chronic inflammatory bowel disease,
- rheumatic diseases (lupus, rheumatoid arthritis),
- malignant processes (Hodgkin's and non-Hodgkin's lymphoma),
- granulomatous diseases: sarcoidosis, histiocytosis X,syphilis, brucellosis, Crohn's disease etc)
- storage diseases (Niemann–Pick disease,Gaucher's disease),
- Parasites (malaria),&
- drugs (methsuximide, griseofulvin, and haloperidol).
Monocytopenia can occur in the context of
- glucocorticoid therapy,
- acute infections,
- aplastic anemia,
- leukemias (acute myeloid leukemia, hairy cell leukemia,&
- drugs (myelotoxic drugs).
It is very likely that your son had a fleeting viral illness that caused the "monocytosis". However, It is better that your son gets a full blood work-up including an absolute monocyte count.That will also help alleviate your continuing anxiety. You may discuss with your doctor who will surely guide you regarding this.
MB BS, MS, FRCS(Edinburgh)