A calcium blood test measures the calcium level in your blood. This test is typically performed with a small sample of blood drawn from a vein in your arm. It can help diagnose medical conditions such as parathyroid disorders and bone, kidney, and thyroid disease.

The test is usually ordered by your primary care physician or a specialist, such as an endocrinologist, and the blood sample is analyzed in a laboratory by a clinical laboratory technologist.

A calcium blood test measures the amount of calcium in your blood to help diagnose and monitor various medical conditions. Calcium is a mineral necessary for many bodily functions, including bone health, muscle function, nerve signaling, and blood clotting.

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

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

Your provider may also order a calcium blood test if you have symptoms of high or low blood calcium levels.

High calcium levels may cause kidney stones, constipation, nausea, vomiting, abdominal pain, appetite loss, increased thirst, and frequent urination. Other potential symptoms include depression, confusion, weakness, fatigue, and bone, joint, and muscle pain.

Symptoms of low calcium levels include dry skin, brittle nails, coarse hair (after extended time), and muscle stiffness or cramps. Other potential symptoms include irregular heartbeat (arrhythmia), seizures, and tingling in the lips, tongue, lips, feet, or fingers.

There are two main tests that healthcare providers use to assess calcium levels in the blood. These include:

Total Calcium Test

This test measures the overall amount of calcium in the blood, including free (ionized) calcium and the calcium bound to proteins. It provides a general overview of calcium levels and is often used as an initial screening tool.

Ionized Calcium Test

This test measures the blood’s levels of free calcium—biologically active calcium that is not bound to proteins. The ionized calcium test is more precise and is often used when the total calcium levels are abnormal or when conditions affecting calcium balance are suspected.

These tests can help healthcare providers learn more about the calcium status in the body. The results enable them to diagnose and manage various medical conditions effectively.

There are usually no special preparations required for a calcium blood test. Your healthcare provider might advise you to temporarily discontinue certain medications or supplements, such as vitamin D, to ensure accurate test results.

You can typically eat and drink as usual before the calcium blood test, but confirm this with your healthcare provider beforehand. If your healthcare provider has ordered additional tests, they will inform you whether you need to fast before your appointment.

Most blood tests only take a few minutes to complete. The collected blood sample is labeled and sent to a laboratory for analysis.

In the lab, the blood sample is tested to measure the total calcium level. They will measure the free (ionized) calcium and calcium bound to proteins.

During the Test

Your calcium blood test will be performed in a clinical laboratory, hospital, or healthcare provider’s office. Wear comfortable, loose-fitting clothing with sleeves that allow easy access to your arms for the blood draw.

A phlebotomist or nurse will take you to a private area to sit for the blood draw. They will:

• Clean the area on your arm with an antiseptic wipe
• Apply a band to your upper arm to contract your veins, making them more visible
• Insert a sterile needle into a vein in your arm to draw a small blood sample (called venipuncture)
• Collect the blood sample into one or more vials
• Remove the needle and apply a bandage or cotton ball to the puncture site

After the Test

Right after the calcium blood test, apply gentle pressure to the puncture site with a cotton ball to stop any bleeding. You can resume your normal activities immediately after the test.

While a calcium blood test is generally considered safe, there are some risks and precautions to be aware of.

The blood draw process may cause temporary discomfort, such as a pinching sensation or mild pain at the puncture site. This discomfort typically resolves quickly. You may also experience minor bruising or bleeding at the puncture site following the blood draw.

A calcium blood draw can yield three types of results: normal, high (or elevated), and low (or decreased) calcium in the blood. Normal results indicate that your calcium levels are within the expected range for a healthy individual. 

If your result is higher or lower than the reference range or if you exhibit symptoms—even with a normal result—your healthcare provider may choose to do further testing to gain a comprehensive understanding of your health status.

Interpreting Your Results

Abnormal findings in a total calcium test can indicate various health conditions. However, abnormal results don’t always necessitate immediate treatment, as factors like diet and medication can influence calcium levels. Discuss any concerns about your results with your healthcare provider for further clarification.

High blood calcium may indicate:

• Excessive vitamin D intake
• Hyperparathyroidism (when your parathyroid glands release too much parathyroid hormone (PTH), a hormone that helps control calcium levels in your blood)
• Certain cancers
• Bone disorders like Paget’s disease

Low blood calcium may indicate:

• Pancreatitis (inflammation of the pancreas)
• Kidney disease (loss of kidney function over time)
• Hypoparathyroidism (when your parathyroid glands don’t release enough PTH)
• Calcium or vitamin D deficiency
• Low blood protein levels due to liver disease, malnutrition, or other causes

Hypercalcemia (high blood calcium level) occurs when calcium levels exceed 10.2 mg/dL. Hypocalcemia (low blood calcium level) is total serum calcium levels below 8.5 mg/dL. Laboratories may vary slightly on ranges for normal levels.

Getting a calcium blood test may seem intimidating, but it’s a routine procedure that helps assess your health. If your results fall outside the normal range, your healthcare provider will explore deeper to understand why.

You might need further testing if your levels are high or low or if you feel unwell despite normal results. Talk to your healthcare provider if you have any questions or concerns.