I see the question all the time, what are the normal reference ranges for XYZ lab tests. The easy answer is it depends on the lab you are using. So, how does a lab determine what is "normal". You probably would have to ask each lab because I am sure there is a method to the madness. A problem, at least maybe for doctors, is that health care consumers are becoming educated on their own health. Michael Kleerekoper, MD, MACE describes on this site that:
What exactly is the problem? If the reference interval for potassium in your institution’s lab is 3.5 mEq/L to 5.4 mEq/L and the patient’s value is 3.4 mEq/L or 5.5 mEq/L, it is highlighted as “abnormal” when the results are posted. Increasingly and appropriately the patient gets a copy of the lab report sent to their home and they can’t miss these abnormal labs.
Read the entire article at Thankful For the Journey