High Yield: Calcium and Bone Disorders for Step 3

• Best indicator of total body vitamin D stores: serum levels of 25-hydroxy vitamin D₃. 
• Primary hyperparathyroidism is the most common cause of hypercalcemia in the outpatient setting; cancer is the most common cause in hospitalized patients.
• Osteomalacia is characterized by decreased bone mineralization and low or normal ionized calcium, normal or high parathyroid hormone, and low vitamin D levels.
• Paget disease should be treated if symptoms are present or if lytic involvement of the vertebrae, skull, weight-bearing bones, or areas adjacent to major joints occurs; bisphosphonates are the therapeutic agents of choice for Paget disease.