One thing to remember is the reference (aka normal range) isn't all people who are healthy and every number not in that range is abnormal and diseased.The reference range for almost everything includes 95% of all healthy people (mean plus or minus two standard deviations from the mean).Usually there is another number which is the "when we get concerned" number. If you took everyone's blood often enough they would eventually be out of the reference range for something.http://www.ehow.com/about_5344433_causes-low-wbc_.html mentions a slightly different reference range (as sometimes each lab adjusts to how their procedures effect the numbers) but the number where the concern starts is 3500 (or 3.5 given how they usually adjust for units) and under 2500 (or 2.5) is where they really start seeing it being dangerously low.Medications may alter the number so it could just be from something you are taking making it look a little low right now.Also most people if you looked have some nodule, cyst or other small thing that will show up on some X-ray or scan. A lot of them are just like a scar from some infection you had sometime in your life or some little bobble in how the organ developed or grew. Depending on how it looks they may do a biopsy or not. Most of the time the "normally abnormal" things look like all the other harmless ones and not like the "dangerously abnormal ones" and get ignored by the doctor because they'd do more damage taking it out/sampling it than the thing causes if you just leave it alone.