What is a Calcium Blood Test?

A calcium blood test measures the amount of calcium in your blood. If there is too much or too little calcium in the blood, it may be a sign of a wide range of medical conditions, such as bone disease, thyroid disease, parathyroid disorders, kidney disease, and other conditions.

Calcium is one of the most important minerals in your body. About 1% of the calcium in your body is in your blood. The rest is stored in your bones and teeth. Having the right amount of calcium in your blood is necessary for your nerves, muscles, and heart to work properly. It also helps blood vessels move blood throughout your body and helps release hormones that affect many body functions.

Other names: total calcium, ionized calcium

What is it used for?

A blood calcium test is used to check your general health. It's also used to help diagnose or monitor many types of medical conditions, including conditions that affect your bones, kidneys, digestive system, thyroid, and parathyroid glands.

There are two types of calcium blood tests that measure different forms of blood calcium:

• Total calcium test measures all the calcium in your blood. You have two types of blood calcium that are normally present in about equal amounts:
  • "Bound calcium" is attached to proteins in your blood.
  • "Free calcium" is not attached to proteins. It's also called ionized calcium. This form of blood calcium is active in many body functions.

  Normally, your body tightly controls the balance of bound and ionized calcium, so a total calcium test gives a good estimate of how much ionized calcium you have.

  A total calcium test is the most common test for blood calcium. It's often part of a basic metabolic panel (BMP) and a comprehensive metabolic panel (CMP), which are both routine screening tests.

• An ionized calcium test measures only the "free calcium" in your blood that isn't attached to proteins. An ionized calcium test is more difficult to do, so it's usually ordered if the results of a total calcium test aren't normal. You may also have this test if you have a condition that affects your body's ability to balance the amounts of ionized and bound calcium in your blood, or if you are seriously ill or having surgery.

Why do I need a calcium blood test?

Your health care provider may have ordered a basic or comprehensive metabolic panel, which includes a calcium blood test, as part of your regular checkup. You may also have this test to diagnose or monitor conditions that can affect your blood calcium or if you have symptoms of abnormal calcium levels.

Symptoms of high calcium levels may include:

• Digestive symptoms, such as:
  • Constipation
  • Nausea and vomiting
  • Abdominal (belly) pain
  • Loss of appetite
• Increased thirst
• Urinating (peeing) more than usual
• Kidney stones
• Bone, joint, and muscle symptoms, such as weakness, aches, and pains
• Fatigue
• A change in mental health, such as depression or confusion

Symptoms of low calcium levels may include:

• Dry skin, coarse hair, and nails that easily break (after a long period of low levels)
• Muscle cramps, spasms, or stiffness
• Tingling in the lips, tongue, fingers, and feet
• Irregular heartbeat (arrhythmia)
• Seizures, if calcium levels are extremely low

Many people with high or low calcium levels don't have any symptoms. So your provider may order a calcium test if you have a known condition that may affect your calcium levels, such as:

• Kidney disease
• Thyroid or parathyroid disease
• Malnutrition
• Problems absorbing calcium
• Certain types of cancer

What happens during a calcium blood test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You usually don't need any special preparations for a calcium blood test or a basic or comprehensive metabolic panel. Your provider may ask you to stop taking certain medicines or supplements, such as vitamin D, to make sure your test results are accurate. If your provider has ordered more tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Results from a total calcium test that are higher than normal may be a sign of many types of conditions, such as:

• Overactive parathyroid glands (hyperparathyroidism), a condition in which your parathyroid glands produce too much parathyroid hormone
• Certain types of cancer, including cancer that spreads to the bone
• Bone disorders, including Paget's disease of the bone
• Taking too much vitamin D over a long period of time

Results from a total calcium test that are lower than normal may be a sign of:

• Low blood protein levels, which may be caused by liver disease or malnutrition
• Underactive parathyroid glands (hypoparathyroidism), a condition in which your parathyroid glands produce too little parathyroid hormone
• Too little calcium in your diet
• Too little vitamin D or magnesium
• Pancreatitis
• Kidney disease

If your results from a total calcium blood test are not in the normal range, it doesn't always mean that you have a medical condition that needs treatment. Your diet and certain medicines can affect your calcium levels. If you have questions about your results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a calcium blood test?

A calcium blood test does not tell you how much calcium is in your bones. Bone health can be measured with a type of x-ray called a bone density scan, or dexa scan. A dexa scan measures the mineral content, including calcium, and other aspects of your bones.