It also could be a WHITE BLOOD COUNT. They want to see how your white blood cells are reacting incase of a infection.
Whole Blood Count...it measures your white blood cells, red blood cells, lymphocytes, leukocytes, monocytes, hematacrit, iron, etc.
It needs to be tested to rule out things like infection, leukemia, lymphoma, and many other problems (those are main three). Lymphnodes could be swollen due to any of those conditions.