Higher than normal levels may be due to a number of health conditions. Common causes include:
- Being on bed rest for a long time
- Taking too much calcium or vitamin D
- HIV/AIDS
- Hyperparathyroidism
- Infections that cause granulomas such as tuberculosis and certain fungal and mycobacterial infections
- Metastatic bone tumor
- Multiple myeloma
- Overactive thyroid gland (hyperthyroidism) or too much thyroid hormone replacement medication
- Paget's disease
- Sarcoidosis
- Tumors producing a parathyroid hormone-like substance
- Use of certain medications such as lithium, tamoxifen, and thiazides
