Bone-specific alkaline phosphatase (BAP) is synthesized by the osteoblasts and is presumed to be involved in the calcification of bone matrix, though its precise role in the formation process is unknown. In the serum of most healthy individuals, bone and liver isoenzymes of the tissue non-specific AP gene predominate in approximately equal proportions. ALP isoenzymes mainly exist in bones, liver, intestine, placenta, mammary glands and kidneys.