A normal range of total blood calcium in adults is usually between 8.5 and 10.3 milligrams/deciliter (mg/dL). Ionized calcium generally should be higher than 4.6 mg/dL to be a normal level.
Blood calcium levels do not indicate levels of bone calcium but rather how much calcium is circulating in the blood.
A normal total or ionized calcium result together with other normal laboratory results generally means that a person’s calcium metabolism is normal and blood levels are being appropriately regulated.
High total calcium (hypercalcemia)
Two of the more common causes of hypercalcemia are:
Hyperparathyroidism, an increase in parathyroid gland function: this condition is usually caused by a benign tumor of the parathyroid gland. This form of hypercalcemia is usually mild and can be present for many years before being noticed.
Cancer: cancer can cause hypercalcemia when it spreads to the bones and causes the release of calcium from the bone into the blood or when a cancer produces a hormone similar to PTH, resulting in increased calcium levels.
Some other causes of hypercalcemia include:
- Prolonged immobilization
- Excess vitamin D intake
- Thiazide diuretics
- Kidney transplant
Low total calcium (hypocalcemia)
The most common cause of low total calcium is:
Low blood protein levels, especially a low level of albumin, which can result from liver disease or malnutrition, both of which may result from alcoholism or other illnesses. Low albumin is also very common in people who are acutely ill. With low albumin, only the bound calcium is low. Ionized calcium remains normal, and calcium metabolism is being regulated appropriately.
Some other causes of hypocalcemia include:
- Underactive parathyroid gland (hypoparathyroidism)
- Inherited resistance to the effects of parathyroid hormone
- Extreme deficiency in dietary calcium
- Decreased levels of vitamin D
- Magnesium deficiency
- Increased levels of phosphorus
- Acute inflammation of the pancreas (pancreatitis)
- Renal failure
Urinary calcium levels may be affected by the same conditions and diseases that affect blood levels (listed above). A high level of calcium in the urine (hypercalciuria) may lead to the formation of crystals or calculi (stones) in the kidneys. About 75% of kidney stones contain calcium.