Calcium (Ca) in Blood Test
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.
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.
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, or inflammation of the pancreas (pancreatitis).
- To find a reason for an abnormal electrocardiogram (EKG) test.
- After a kidney transplant.
- To see if your symptoms may be caused by a very low calcium level in the blood. Such symptoms may include muscle cramps, spasms, and twitching and tingling in the fingers and around the mouth.
- 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 can't 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 density, check the amount of calcium in the bones.
How To Prepare
In general, you don't need to prepare before having this test. Your doctor may give you some specific instructions.
How It Is Done
A health professional uses a needle to take a blood sample, usually from the arm.
How It Feels
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
Normal blood calcium values are lower in older people.
You may also have values for an ionized calcium test. This test checks the amount of calcium that is not attached to protein in the blood. The level of ionized calcium in the blood is not affected by the amount of protein in the blood.
High values of calcium may be caused by:
- Cancer, including cancer that has spread to the bones.
- Being on bed rest for a long time.
- Paget's disease.
Low values of calcium may be caused by:
- A low level of the blood protein albumin (hypoalbuminemia).
- High levels of phosphate in the blood. This can be caused by kidney failure, laxative use, and other things.
- Malnutrition caused by diseases such as celiac disease, pancreatitis, and alcohol use disorder.