Author: John Winkler, M.D.  Educational Pearls Normally, the parathyroid is the master regulator of serum Ca levels. It secretes PTH, which stimulates calcium uptake from the bone and gut. Causes of hypercalcemia include: parathyroid tumor, lytic bone lesions (multiple myeloma), breast cancer, renal injury, and some lung cancers. Hypercalcemia can lead to poor bone quality and pathological fractures. It can also cause heart arrhythmias. It is important to order an ionized calcium to quantify the level of hypercalcemia, since calcium binds to albumin. Treatment for hypercalcemia includes fluids and loop diuretics. References:  https://emedicine.medscape.com/article/766373-treatment