- Last Update On : 2013-01-01
Plasma calcium exists in the blood in three forms; 50% is ionized, 40-45% is protein bound, and 5-10% is complexed to anions such as bicarbonate, citrate, sulfate, phosphate, and lactate. Plasma ionized calcium is the biologically active moiety. Total calcium levels are maintained between 8.8 and 10.2 mg/dL. Parathyroid hormone and vitamin D regulate normal plasma calcium levels by their actions on kidney, intestine, and bone ion transport.
The main causes of hypercalcemia are primary hyperparathyroidism, malignant disease, and chronic renal failure. The differential diagnosis of hypercalcemia depends on the clinical setting. Overall, primary hyperparathyroidism and malignancy account for 80 – 90% of hypercalcemia cases. However, primary hyperparathyroidism is the cause of ~60% of ambulatory cases and of ~25% of inpatient cases, whereas malignancy causes ~35% of ambulatory cases and 65% of inpatient cases.
Malignancies can raise serum calcium levels by either direc