My asthma doctor said my white blood cell count is a little low. I m 55 yrs old and I do get the occasional illnesses (cold, sinus infection, stomach virus) but my asthma is under control. Since I was concerned, I ordered copies of my bloodwork from the lab, covering the past 6 months and my wbc range anywhere from 4,000 to 4,600. I thought that range is considered normal. Should I be concerned?