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Calcium (Ca) in Blood

Test Overview

A test for calcium in the blood checks the calcium level in the body that is not stored in the bones. Calcium is the most common mineral in the body and one of the most important. The body needs it to build and fix bones and teeth, help nerves work, make muscles squeeze together, help blood clot, and help the heart to work. Almost all of the calcium in the body is stored in bone.

Normally the level of calcium in the blood is carefully controlled. When blood calcium levels get low (hypocalcemia), the bones release calcium to bring it back to a good blood level. When blood calcium levels get high (hypercalcemia), the extra calcium is stored in the bones or passed out of the body in urine and stool. The amount of calcium in the body depends on the amount of:

Vitamin D and these hormones help control the amount of calcium in the body. They also control the amount of calcium you absorb from food and the amount passed from the body in urine. The blood levels of phosphate are closely linked to calcium levels and they work in opposite ways: As blood calcium levels get high, phosphate levels get low, and the opposite is also true.

It is important to get the right amount of calcium in your food because the body loses calcium every day. Foods rich in calcium include dairy products (milk, cheese), eggs, fish, green vegetables, and fruit. Most people who have low or high levels of calcium do not have any symptoms. Calcium levels need to be very high or low to cause symptoms.

Why It Is Done

A blood calcium test may be done:

  • To check for problems with the parathyroid glands or kidneys, certain types of cancers and bone problems, or inflammation of the pancreas (pancreatitis).
  • To find a reason for an abnormal electrocardiogram (EKG) test.
  • After a kidney transplant.
  • To see if your symptoms may be caused by a very low calcium level in the blood. Such symptoms may include muscle cramps, spasms, and twitching and tingling in the fingers and around the mouth.
  • To see if your symptoms may be caused by a very high calcium level in the blood. Such symptoms may include weakness, lack of energy, not wanting to eat, nausea and vomiting, constipation, urinating a lot, belly pain, or bone pain.
  • As part of a routine blood test.

A blood calcium test can't be used to check for a lack of calcium in your diet or for the loss of calcium from the bones (osteoporosis). The body can have normal calcium levels even if your diet does not have enough calcium in it. Other tests, such as bone mineral density, check the amount of calcium in the bones.

How To Prepare

Do not take calcium supplements for 8 to 12 hours before having a blood calcium test. Your doctor will tell you if you should not eat or drink anything before your test.

How It Is Done

The health professional drawing blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure to the site and then a bandage.

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

There is very little chance of a problem from having a blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
  • Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (such as Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

A test for calcium in the blood checks the calcium level in the body that is not stored in the bones.

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Total calcium1
Adults:

8.8–10.4 milligrams per deciliter (mg/dL) or 2.2–2.6 millimoles per liter (mmol/L)

Children:

6.7–10.7 milligrams per deciliter (mg/dL) or 1.90–2.75 millimoles per liter (mmol/L)

Normal blood calcium values are lower in older people. Normal blood calcium values are higher in children because their bones are growing quickly.

An ionized calcium test checks the amount of calcium that is not attached to protein in the blood. The level of ionized calcium in the blood is not affected by the amount of protein in the blood.

Ionized calcium1
Adults:

4.65–5.28 mg/dL or 1.16–1.32 mmol/L

Children:

4.80–5.52 mg/dL or 1.20–1.38 mmol/L

High values

High values of calcium may be caused by:

Low values

Low values of calcium may be caused by:

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Taking calcium or vitamin D in any form including milk, antacids, or supplements right before the test.
  • Taking medicines, such as diuretics. Many medicines can affect calcium levels in the blood.
  • Having dialysis.
  • Having a high volume blood transfusion or many blood transfusions in a short period of time.

What To Think About

  • More than one blood test may be needed to see if blood calcium levels are not normal.
  • Low blood levels of calcium may be caused by low levels of protein (albumin) in the blood, because about half of all calcium in the blood is attached to albumin. For this reason, an ionized calcium level (which is not attached to albumin) and a blood albumin level may also be measured. To learn more, see the topic Total Serum Protein.
  • Other tests that may be done to find the cause of abnormal blood calcium levels include blood tests for parathyroid hormone (PTH), chloride, acid phosphatase, alkaline phosphatase, and vitamin D.
  • Calcium levels can also be checked in the urine. To learn more, see the topic Calcium (Ca) in Urine.

References

Citations

  1. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

Credits

By Healthwise Staff
E. Gregory Thompson, MD - Internal Medicine
Christopher G. Wood, MD, FACS - Urology, Oncology
Last Revised September 24, 2012

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

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