Alkaline Phosphatase (Definition). The normal range is 20 to 140 iu/l.[12] high levels can indicate active bone formation occurring as alp is a byproduct of osteoblast activity (such as the case in paget's disease of bone).lkaline Phosphatase (Definition). The normal range is 20 to 140 iu/l.[12] high levels can indicate active bone formation occurring as alp is a byproduct of osteoblast activity (such as the case in paget's disease of bone).