Calcium is important because it is needed for strong bones. Your muscles, nerves and heart need calcium to work properly, while calcium also helps your blood to clot.
What is being tested?
Almost all the calcium in your body is found in your bones and teeth; the rest of it is found in your blood.
You lose some calcium every day in your urine. Your doctor might also test your urine to find out how much calcium your kidneys are excreting.
Why would I need this test?
There are many possible reasons why you might need a calcium blood test.
If you are tired, weak, thirsty, have lost your appetite, need to urinate a lot, are constipated or have pain in the abdomen, your doctor might suspect you have too much calcium in your blood.
They might suspect you have too little calcium in your blood if you get numbness around your mouth and in the hands and feet, or if you get muscle spasms.
A blood test for calcium can be part of routine testing if you have or are suspected of having:
- kidney disease
- kidney stones
- bone disease
- thyroid disease or growths near the thyroid
- intestinal diseases
- some types of cancer
- poor nutrition
You might need repeated tests for calcium if:
- you have kidney disease
- you've had a kidney transplant
- you're being treated with calcium or vitamin D supplements
- you have some types of cancer, especially those that affect the bones
How to prepare for the test
Your doctor might ask you to stop taking medicines such as antacids, diuretics and vitamin D supplements. These all either contain calcium or affect how much calcium there is in your blood.
Apart from this, no preparation is necessary.
Understanding your results
A calcium test provides information about how much calcium is in your blood, but it doesn’t tell you about the calcium in your bones.
You need to talk to your doctor to properly understand the results of your test, and to find out what comes next.
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Last reviewed: June 2020