Causes of High Bone Alkaline Phosphatase

ABSTRACT Serum alkaline phosphatase (ALP) is a member of a family of zinc metalloprotein enzymes that function to split off a terminal phosphate group from an organic phosphate ester. Many things may cause increases of ALP activity in serum, the most common being obstructive liver disease and metabolic bone disease. An increase of the liver or particularly the bone isoform (bone specific ALP) in serum can provide valuable diagnostic information. Bone specific alkaline phosphatase isoenzyme is elevated as a result of increased osteoblastic activity. The highest total ALP values have been attributed to an increased bone isoenzyme level due to Paget disease or rickets/osteomalasia. The enzyme activity, which is localized in the plasma membrane of osteoblasts before extracellular release, correlates with the extent of the disease on skeletal surveys and with parameters of bone resorption. This isoenzymes is normally elevated in growing children and adults over the age of fifty. Causes of high bone ALP include bone growth, healing fracture, acromegaly, osteogenic sarcoma, or bone metastases, leukemia, myelofibrosis, and rarely myeloma; so ALP is used as a tumor marker. Hyperthyroidism, by its effects upon bone, may also elevate ALP. We presented two patients have raised alkaline phosphatase. Isoenzyme studies confirmed its bony origin.