White Blood Count (CBC) - White blood cells fight infection; if you have too few, you may not be able to fight infection.   A rise in the number of white blood cells may mean that there is a bacterial infection in your body.  In contrast, a very low white blood cell count may result from a viral infection.  A side effect of the medications used to prevent or treat organ rejection is a lowering of the WBC.  Thus, the WBC is regularly monitored to detect infection or overdosing of medication.  Normal WBC is 4,300-10,800.