My son has had high grade fever since 2 days. His CBC shows Wbc at the low end @ 4.9 and high monocyte @11.5. What does this indicate?

High monocyte count. Hi, I am assuming your son has been seen and evaluated by his pediatrician? Did he/she order the bloodwork? Most likely, with limited information, a high monocyte count with fever can be due to a viral infection, which most likely is self limited. Normally, I would repeat the cbc when he is healthy again. Also, I recommend you call his pediatrician just to confirm that this is his opinion also.