Calcium blood test — how does it work?

If you have had a calcium blood test or you’ve been advised to take one, you may have questions about how the test works and what it may tell your healthcare provider. A calcium blood test can provide valuable health information.

A calcium blood test measures the amount of calcium that's circulating in the blood. 

Calcium is an essential mineral for our health. It's the most abundant mineral in the body, comprising much of our bones and teeth. In the body, it helps blood vessels, muscles and nerves function properly. It also plays a role in blood clotting and hormone secretion. About 98% of the calcium in our bodies is stored in our bones. The remaining calcium can be found in our muscles, blood and other tissues. A calcium blood test tells your healthcare provider if you have normal calcium levels in your blood. 

There are two ways to measure blood calcium:

• Total calcium: This measures all the calcium in your blood, including calcium that is attached to protein and ionized calcium that is unattached. A total calcium blood test may be done as part of a regular checkup.

• Ionized calcium: This measures the calcium that is not attached to protein.

Your healthcare provider will let you know if there are specific instructions you should follow to prepare for the test. For example, they may want you to fast (not eat) beforehand. A healthcare practitioner will take blood from a vein in your arm, using a small needle. The process is relatively painless and usually takes no more than five minutes. The blood sample will then be sent to a lab to be analyzed, and your healthcare provider will deliver the results to you.

There is minimal risk in having your blood calcium level tested, other than the potential for bruising or slight pain where the needle enters your skin.

A calcium blood test can help your healthcare provider diagnose certain health conditions. 

A calcium blood test is commonly ordered during your regular checkup as part of a basic metabolic panel (BMP). A BMP is a blood test that measures several factors in your blood and provides your healthcare provider with information about your current level of health. 

Additionally, your healthcare provider may order a calcium blood test as a way to help diagnose certain conditions or monitor diseases you may already have. Kidney diseases, parathyroid gland disease, pancreatitis, malnutrition and certain types of cancer may all cause abnormal blood calcium levels. If your healthcare provider is concerned that you have one of these conditions or is watching an already diagnosed illness, they will likely use this test as part of their exam.

Most people will not have symptoms of abnormal blood calcium levels. However, the following symptoms may occur, prompting your healthcare provider to order a blood calcium test. 

Symptoms of high calcium levels include: 

• Abdominal pain 

• Constipation

• Increased thirst 

• Increased urination 

• Kidney stones 

• Loss of appetite 

• Nausea and vomiting 

Low calcium level symptoms include: 

• Irregular heartbeat 

• Muscle cramps and spasms 

• Seizures 

• Tingling of hands, feet, lips or tongue 

Your healthcare provider will go over your results with you and share any concerns they have about your blood calcium levels. Additional testing may be needed to help correctly diagnose a condition.  

High calcium levels (called hypercalcemia) may indicate the following conditions: 

• Certain types of cancer 

• High intake of calcium or vitamin D in the form of food or supplements 

• Hyperparathyroidism — a condition of the parathyroid gland 

• Overuse of calcium antacids (a type of over-the-counter medication used to treat heartburn) 

• Paget's disease — a disease of the bones 

Low calcium levels (called hypocalcemia) may indicate the following conditions: 

• A deficiency in vitamin D or magnesium

• Hypoparathyroidism — a condition of the parathyroid gland 

• Kidney disease 

• Pancreatitis 

It's important to know that abnormal blood calcium levels do not necessarily mean that you have a medical condition. Diet and certain medications can affect calcium levels in your blood, and your healthcare provider will consider this when reviewing the results.  

It should also be noted that a blood calcium test is not used to assess the amount of calcium in your bones. A bone scan is needed to look at the health of your bones.  

If you’re concerned about your calcium levels or you’re considering taking calcium supplements, talk to your healthcare provider. 

Published March 2022.