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Alkaline Phosphatase High Bone Disease

Alkaline phosphatase is an enzymatic protein found in bone, liver, intestine and placenta. Levels are elevated in the following bone related conditions: physiologic bone growth, Paget disease, osteomalacia and rickets, osteosarcoma and bone metastasis.

  1. Physiologic Bone Growth

    • Normal bone growth is accomplished by the action of two types of cells: osteoblasts and osteoclasts. Osteoblasts are responsible for laying down new bone and osteoclasts are responsible for breaking down bone. During bone growth, there is increased activity of both types of cells. Thus, with higher activity of osteoclasts, there is more alkaline phosphatase released from the breakdown of bone.

    Paget Disease

    • Paget disease is due to abnormally high activity of osteoclasts. The result is abnormal rates of bone breakdown. Pain and skeletal deformities are the most common indications of this disease. However, asymptomatic individuals may be incidentally identified based on elevated alkaline phosphatase levels on routine analysis.

    Osteomalacia and Rickets

    • Vitamin D deficiency prevents deposition of calcium to newly formed bone. When this occurs after the bony growth plates have closed, the disorder is referred to as osteomalacia. When it occurs before closure of growth plates it is referred to as rickets. Symptoms of osteomalacia include pain and weakness. In children, rickets causes soft bones that leads to deformities that persist into adulthood.

    Bone Sarcomas

    • Bone sarcomas are a very rare cause of bone disease. According to "Harrison's Principles of Internal Medicine," bone sarcomas accounted for only 0.2 percent of new cases of malignant cancer in 2007. The common bone sarcomas are osteosarcoma, chondrosarcoma and Ewing's sarcoma.

    Bone Metastasis

    • Metastasis to bone is a secondary cause of alkaline phosphatase high bone disease. The most common cancers that metastasize to bone are carcinomas of the breast, lung and prostate. Symptoms of metastatic bone disease include bone pain, swelling and/or fracture.

    Other Causes of Increased Alkaline Phosphatase

    • Alkaline phosphatase is also elevated in obstructive diseases of the biliary system, liver disease, hyperparathyroidism, hyperphosphatemia, gastrointestinal diseases, hyperthyroidism and with use of drugs that are toxic to the liver.

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