Normal range ,Critical and Reference values are terminology related to lab tests that most laboratory specialist should be familiarize with.
Normal range is usually established by testing a large population of healthy individuals. There is usually a range of “normal.”
Reference range : This vary with age and gender (e.g., creatinine tends to be higher in males especially those with larger muscle,ESR turn to be greater in elderly people).
Critical Values : These are values that alert the laboratory technician to make prompt clinical intervention and may be considered as cases of Emergency. Critical results are dangerously abnormal values and must be reported to the laboratory technician in charge or the medical doctor, and the lab usually makes note of that for a rapid intervention in order to remedy the situation. (E.g Hb level low than 5mg/dl, FBS level higher than normal)