Calcium (Ca) in Blood
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:
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 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:
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 mineral density, check the amount of calcium in the bones.
How To Prepare
Do not take calcium supplements for 8 to 12 hours before having a blood calcium test. Your doctor will tell you if you should not eat or drink anything before your test.
How It Is Done
The health professional drawing blood will:
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
A test for calcium in the blood checks the calcium level in the body that is not stored in the bones.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Normal blood calcium values are lower in older people. Normal blood calcium values are higher in children because their bones are growing quickly.
An ionized calcium 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:
Low values of calcium may be caused by:
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
What To Think About
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