What Is a Calcium Blood Test?

A calcium blood test is used to measure the amount of calcium you have in your blood. There are two types of calcium blood tests: a total calcium blood test and an ionized calcium blood test.

A large portion (about half) of the calcium in the body is bound to proteins like albumin. A total calcium blood test measures the calcium concentration of all the calcium in the blood, both bound and unbound. With an ionized calcium blood test, the only the calcium in your blood that is unbound to proteins is measured.

Both tests are performed the same way, but a total calcium blood test is more commonly performed. Learn more about what to expect with a total calcium blood test.

Purpose of Test

Calcium is a very important mineral, necessary for strong and healthy bones and teeth. Calcium also contributes to the proper functioning of your heart, muscles, and nerves. So, it makes sense why a calcium blood test would be an important test to undergo.

Your healthcare provider will order a total calcium blood test as part of your regular medical checkup. A total calcium blood test may also be ordered if you are exhibiting symptoms related to high or low calcium levels.

Some of the symptoms of high calcium levels are:

• Nausea and/or vomiting
• Peeing more frequently than normal
• Constipation
• Lack of appetite
• Fatigue
• Increased thirstiness

Some of the symptoms of low calcium levels are:

• Cramps in your muscles and stomach
• Tingling in your fingers, feet, and lips
• Having an irregular heartbeat

Some medical conditions are known to affect calcium levels, so if you have any of them (or are suspected to have any of them), your healthcare provider may order a calcium blood test to diagnose or monitor the condition:

• Kidney disease: People with kidney disease usually have low calcium levels.
• Parathyroid disorder
• Thyroid disease
• Kidney stones
• Malabsorption: (the inability of your body to properly absorb the vitamins and nutrients it needs from the food you eat)
• Cancer: (breast cancer, lung cancer, head and neck cancer, multiple myeloma, and kidney cancer)
• Malnutrition: This is when you're either not eating enough or not eating the right kinds of foods that will provide your body with the nutrients it needs. When you are malnourished, your calcium levels will likely be very low.

Finally, if you already being treated for having abnormal calcium levels, your healthcare provider may order this test to monitor the effectiveness of your treatment plan.

Other Accompanying Tests

Many times, a total calcium blood test will be ordered along with other tests in a basic metabolic panel (a test that measures important minerals and substances in the body). Some of the tests in a basic metabolic panel are a glucose test, creatinine test, and sodium test. For a more in-depth analysis of your medical status, your practitioner may order a total calcium test in combination with the tests in a comprehensive metabolic panel.

Ionized calcium tests are more expensive and more technical, which generally makes them more difficult to carry out. However, in some cases, your healthcare provider may order an ionized calcium test instead of a total calcium test if:

• you have abnormal albumin levels
• you are critically ill and/or are about to undergo a major surgery
• you are undergoing a blood transfusion
• you are receiving large amounts of IV fluid
• you have late stage chronic kidney disease

Risks and Contraindications

A calcium blood test, like most other blood tests, doesn’t have any contraindications or serious risks.

Before the Test

Your healthcare provider will ask you questions about your medical history. He or she will also likely ask questions about your family medical history. You should disclose to your practitioner if you have a family history of kidney disease or thyroid disease.

It's also best to tell your practitioner about all the medication, supplements, and/or herbs you may be taking. You should let your healthcare provider know if you are (or could be) pregnant as it may affect your calcium levels, and therefore, your results.

Timing

The calcium blood test is a simple blood test and will take only about a minute or two.

Location 

The test will take place in the hospital. This could either be in the laboratory of the hospital or in your practitioner's office.

What to Wear 

You can dress as you like for these tests. Although, it would be advisable to wear sleeveless or short sleeved clothes, or at the very least, clothes with sleeves that are easily rolled. This makes for easy access as the blood will be drawn from your arm.

Food and Drink 

There is no food restriction with this test; however, if your healthcare provider is ordering it along with other tests, she may instruct you not to eat or drink anything for some hours before.

What to Bring

You will be able to drive or transport your self back home after this test, so there’s no need to ask a friend or family member to pick you up.

During the Test

The blood draw will be performed by either your healthcare provider, a nurse, or a laboratory scientist. A needle will be injected into your arm, and blood will be drawn from it. The blood drawn will be transferred into the appropriate test tube or vial. 

You may feel a little stinging while the needle is inserted and while it’s being used to pull blood, but that’s normal. If your veins are hard to see, a tourniquet may be tied around your arm for some seconds. This will allow your veins become more prominent and easier to see.

This entire process will take just a minute or two. If you feel any serious pain during this process, you should immediately tell the practitioner, nurse, or whoever is drawing the blood.

After the Test

Once your blood has been taken, you’re free to leave. If you feel a bit dizzy or faint, you should sit for a few minutes and let it pass before you attempt to drive. 

You’ll likely be informed of the specific date to come back for the test results.

Managing Side Effects 

Blood tests are generally safe and the few side effects that may occur usually go away within hours, or at worst, a day or two. The common side effects are:

• Slight bruising or swelling where the needle was inserted
• Mild stinging or throbbing

Although rare, a couple of more serious side effects could develop and you should let your healthcare provider know immediately if you have them. These include:

• Infection
• A lump of blood under the skin (also called a hematoma and usually caused by a blood vessel that has been injured)
• Serious/excessive bleeding at the site of the injection

If you suspect that you may be experiencing any of these effects, be sure to call your practitioner or the healthcare professional who performed the test.

Interpreting Results

Your healthcare provider or the attendant at the lab will be the one to tell you how long it’ll take for your results to arrive. Normal calcium levels are between 8.5 to 10.2 mg/dL (milligram per decilitre). 

You should know that there are certain drugs that can affect the test results. However, your practitioner will likely have instructed you to stop taking them before the test, if necessary. Some of these drugs are:

• Thiazide diuretics
• Lithium
• Tamoxifen
• Calcium salts
• Thyroxine
• Vitamin D supplements

Another factor that could influence your test results includes being immobilized or bedridden for a long period of time beforehand. Additionally, drinking large quantities of milk beforehand can likely skew your results.

Follow-Up 

A higher than normal total calcium (hypercalcemia) could be indicative of having any of the following conditions.

• Hyperparathyroidism: With hyperparathyroidism, one of your four parathyroid glands is producing too much of the parathyroid hormone. If your healthcare provider suspects this, he/she will order a repeat total calcium test and another blood test to check for your parathyroid hormone levels. If further tests reveal elevated levels, then a diagnosis of hyperparathyroidism will likely be made.
• Paget's Disease: Paget's disease is a disorder in which your bones are enlarged and weak. If your practitioner suspects this after considering your calcium test results and your symptoms, he will order an X-ray and bone scan, along with a blood test to measure your serum alkaline phosphate, before making a diagnosis.
• Cancer: Lung cancer, breast cancer, and some blood cancers can cause hypercalcemia. If your healthcare provider suspects that you have cancer, he will order the appropriate tests—further blood tests and biopsies—to check for the presence of malignancies.
• Hyperthyroidism: This is a condition in which your thyroid is overactive and producing too much of the thyroid hormone. Hyperthyroidism is diagnosed by ordering a thyroid stimulating hormone (TSH) test. Thyroxine (T4) and triiodothyronine (T3) tests may also be ordered, too.
• Sarcoidosis: This is a rare condition in which tiny clumps of inflammatory cells grow in different parts of your body. It is difficult to diagnose and there are a myriad of tests—from a physical exam, chest X-rays, to CT scans—that your healthcare provider may order if there is a chance you have sarcoidosis.
• Excess Vitamin D Intake

A lower than normal total calcium test result could indicate the presence of any of these conditions:

• Hypoparathyroidism: Hypoparathyroidism is one of the most common underlying causes of calcium levels, and it is caused when your parathyroid glands aren’t functioning well and are not producing enough parathyroid hormones (or any at all). If your practitioner suspects this is the case, he will order blood tests to check for your phosphorus and parathyroid hormone levels.
• Kidney Disease: If your healthcare provider suspects that you have kidney disease, he will order a blood test called an estimated glomeruli function test (eGFR) to check how well your kidneys are functioning.
• Acute Pancreatitis: This is a condition in which the pancreas suddenly gets inflamed before eventually recovering. To make a diagnosis of acute pancreatitis, your practitioner will order blood tests to measure your blood levels of magnesium, potassium, sodium, sugar, and fats.
• Low-Protein Levels: A low total calcium result can mean you have low protein levels, especially of the protein albumin. Low levels of albumin could be indicative of liver disease and other serious conditions. Because of this, your healthcare provider may order an albumin blood test to check what your levels of albumin actually are.
• Magnesium deficiency: To confirm a diagnosis of this, your practitioner will likely order a blood test measuring your magnesium levels. This test is usually contained in a basic metabolic panel test.
• Vitamin D Deficiency

You should note that having a calcium test result that is outside the normal range doesn’t mean for sure that you have any medical condition. You should discuss thoroughly with your healthcare provider what your results mean and what they may or may not indicate.

The calcium tests result, along with other test results and your symptoms (if any), that your practitioner may make a diagnosis of any underlying medical conditions.

If you underwent the total calcium test to monitor a condition you have already been diagnosed with, you should ask your healthcare provider what the test results are indicative of—is your condition getting better or is it getting worse? Will you need to add more steps or medications to your treatment plan? You should also ask if you will need to take this test at regular intervals.

A Word From Verywell

It may be a couple of days before your calcium blood test results are ready, and during that period, you may feel anxious or nervous. You should speak to your family and friends about your fears as that may make you feel better. Another important thing you should know is that regardless of your results, a calcium blood test is rarely enough to make a decisive diagnosis of any serious medical condition.

If based on your calcium test results, your healthcare provider suspects you have another underlying condition, you will still have to undergo further tests to confirm the condition's presence or absence. If it does turn out that you do have an underlying condition causing your abnormal calcium levels, it’s best that it was caught early so that treatment can be most effective.