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Calcium (Ca) in Blood

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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.

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.

WebMD Medical Reference from Healthwise

Last Updated: September 24, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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