Serum alkaline phosphatase levels are increased in:

Laboratory Findings in Paget's disease: The serum calcium and serum phosphorus levels are usually within normal limits, even in cases of advanced osteitis deformans. The serum alkaline phosphatase level may be elevated; however, to extreme limits. Values as high as over 250 Bodansky units have been reported, particularly in patients in the osteoblastic phase of the disease, when there is rapid formation of new bone and when there is polyostotic involvement. In fact, there is no other disease of bone in which the serum alkaline phosphatase level may be as high as in Paget’s disease. Ref: Shafer's textbook of oral pathology 7th edition page 733