High calcium concentration in the blood means that the concentration of calcium ions in the blood is outside the normal range. Clinically, high blood calcium levels can be caused by a variety of reasons, the most common of which is a problem with the endocrine organs that regulate calcium ions, because human blood calcium is mainly regulated by the parathyroid glands, which secrete parathyroid hormones that can effectively increase blood calcium levels. When the parathyroid hormone function is hyperactive, the blood calcium concentration will increase significantly, such as secondary hyperparathyroidism caused by parathyroid adenoma and other tumors, which may cause abnormally high calcium ion concentration. In addition, blood system diseases can also cause an increase in calcium concentration, the most common being multiple myeloma, which secretes large amounts of osteoclasts, causing osteoclasts to activate, causing calcium ions to be shed from the bones and enter the serum, also causing an abnormal increase in calcium ion concentration.