Calcium is the most plentiful mineral in your body. Your body uses it to:
- Strengthen your bones and teeth
- Contract your muscles
- Narrow and widen blood vessels
- Send and receive nerve messages
- Release hormones
- Clot your blood
Almost all of your body's calcium is stored in your bones. A very small amount -- about 1% -- is in your blood. Calcium in your blood comes in two forms:
- Free calcium is not attached to anything else in your blood.
- Bound calcium is attached to a protein called albumin or other substances in your blood.
There are two types of blood calcium tests:
- A total calcium test measures both free and bound calcium. It's the type of blood calcium test doctors order most often.
- An ionized calcium test measures only free calcium.
When Would I Get This Test?
You might get a calcium blood test if you have a disease that can affect your levels of this mineral, such as:
- Bone disease (osteoporosis, for example)
- Cancer of the breast, lung, kidney, head, and neck, or multiple myeloma
- Kidney or liver disease
- Nerve problem
- Overactive thyroid gland
- Pancreatitis, which is inflammation of the pancreas
- Parathyroid disease, in which glands in your neck are either too active or not active enough, causing unhealthy levels of calcium in your blood
- Problem absorbing nutrients from food in your intestines
This test can check how well your body is reacting to treatments for some of these conditions. And, it can be used to monitor the side effects of medicines you take.
Another reason to get this test is if you have symptoms of high calcium, which include:
Or if you have symptoms of low calcium, like these:
How Do I Prepare?
Tell your doctor about all the medicines you take -- even medications you bought over the counter (without a prescription). Some medications can affect the results of your calcium blood test.
Your doctor might ask you to stop taking these medicines before the test:
What Happens During the Test?
A lab tech will take a sample of blood from a vein in your arm. You might feel a pinch where the needle goes in. She’ll cover the site with a bandage.
Your arm may be a little sore or bruised where the blood was drawn. Some people become lightheaded for a few moments.
What Do the Results Mean?
Your doctor will send your blood sample to a lab for testing. You should get the results in a few days.
Normal blood calcium results in adults are:
- Total blood calcium: 8.5 to 10.3 milligrams per deciliter (mg/dL)
- Ionized calcium: higher than 4.6 mg/dL
High total calcium levels can be caused by:
- Overactive parathyroid or thyroid gland
- Sarcoidosis -- an inflammatory disease that causes growths to form around your body
- Tuberculosis -- a lung disease caused by bacteria
- Staying in bed for too long
- Too much vitamin D in your diet
- High blood pressure medications called thiazide diuretics
- Kidney transplant
Low total calcium levels may be caused by:
- Low protein levels in your blood
- Underactive parathyroid gland
- Along with too little calcium, low levels of magnesium and/or vitamin D in your body
- Too much phosphorus
- Kidney failure
If your calcium level is too low or high, your doctor might order one of these other tests to find the cause:
- Kidney function tests
- Parathyroid hormone level
- Phosphorous level
- Vitamin D level
Test results can differ slightly by lab. Talk to your doctor about the meaning of your test results. Find out what other tests you should have, and what to do next.