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Calcium (Ca)
A test for calcium in the blood checks the calcium level in the body that is not stored in the bones. Calcium is the most common mineral in the body and one of the most important. The body needs it to build and fix bones and teeth, help nerves work, make muscles squeeze together, help blood clot, and help the heart to work. Almost all of the calcium in the body is stored in bone. The rest is found in the blood.

Normally the level of calcium in the blood is carefully controlled. When blood calcium levels get low (hypocalcemia), the bones release calcium to bring it back to a good blood level. When blood calcium levels get high (hypercalcemia), the extra calcium is stored in the bones or passed out of the body in urine and stool. The amount of calcium in the body depends on the amount of:
- Calcium you get in your food.
- Calcium and vitamin D your intestines absorb.
- Phosphate in the body.
- Certain hormones, including parathyroid hormone, calcitonin, and estrogen in the body.

A blood calcium test may be done:
- To check for problems with the parathyroid glands or kidneys, certain types of cancers and bone problems, inflammation of the pancreas (pancreatitis), and kidney stones. Abnormal results on an electrocardiogram (EKG) test may be caused by high or low calcium levels. - To see if your symptoms may be caused by a very low calcium level in the blood. Such symptoms may include muscle cramps and twitching, tingling in the fingers and around the mouth, muscle spasms, confusion, or depression. - To see if your symptoms may be caused by a very high calcium level in the blood. Such symptoms may include weakness, lack of energy, not wanting to eat, nausea and vomiting, constipation, urinating a lot, belly pain, or bone pain. - As part of a routine blood test.