My son had a low white blood count and high monocyte. is that sepsis?

Not likely: Monocytosis is consistent with a viral process. The finding will require further followup. If monocytosis persists the patient may need to see a hematologist and a bone marrow evaluation done. Sepsis is a bacterial infection in the blood stream and other organs. The white cells are of a different population than monocytes in sepsis.

Not necessarly: Sepsis is an active infection associated with a heightened immune response and can't be defined by white blood counts only. Some viral infections can have this pattern.