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.

Vitamin D and these hormones help control the amount of calcium in the body. They also control the amount of calcium you absorb from food and the amount passed from the body in urine. The blood levels of phosphate are closely linked to calcium levels and they work in opposite ways: As blood calcium levels get high, phosphate levels get low, and the opposite is also true.

It is important to get the right amount of calcium [at least 1000mg a day] in your food because the body loses calcium every day. Foods rich in calcium include dairy products (milk, cheese), eggs, fish, green vegetables, and fruit. Most people who have low or high levels of calcium do not have any symptoms. Calcium levels need to be very high or low to cause symptoms.

Why It Is Done

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.

A blood calcium test cannot be used to check for a lack of calcium in your diet or for the loss of calcium from the bones (osteoporosis). The body can have normal calcium levels even if your diet does not have enough calcium in it. Other tests, such as bone mineral density, check the amount of calcium in the bones.