How the Test is Performed

A blood sample is needed. For information on how this is done, see: Venipuncture.

How to Prepare for the Test

You should not eat or drink for at least 6 hours before the test. Your doctor may tell you to temporarily stop taking any drugs that can affect the test results. Calcium salts, hydralazine, lithium, thiazide diuretics, and thyroxine can increase your level of ionized calcium.

Never stop taking any medicine without first talking to your doctor.

Why the Test is Performed

Your doctor may order this test if you have signs of kidney or parathyroid disease. The test may also be done to monitor persons who have already been diagnosed with such diseases.

Usually, blood tests measure your total calcium level, which looks at both ionized calcium and calcium attached to proteins. You may need to have a separate ionized calcium test if you have factors that increase or decrease total calcium levels, such as abnormal blood levels of albumin or immunoglobulins.

Normal Results

• Children: 4.4 - 6.0 milligrams per deciliter (mg/dL)
• Adults: 4.4 - 5.3 mg/dL

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What Abnormal Results Mean

Higher-than-normal levels of ionized calcium may be due to:

• Decreased levels of calcium in the urine from an unknown cause
• Hyperparathyroidism
• Lack of mobility
• Milk-alkali syndrome
• Multiple myeloma
• Paget's disease
• Sarcoidosis
• Thiazide diuretics
• Tumors
• Vitamin D excess

Lower-than-normal levels may be due to:

• Hypoparathyroidism
• Malabsorption
• Osteomalacia
• Pancreatitis
• Renal failure
• Rickets
• Vitamin D deficiency

Alternative Names

Free calcium; Ionized calcium

References

Bringhurst FR, Demay MB, Kronenberg HM. Hormones and disorders of mineral metabolism. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 28.

Wysolmerski JJ, Insogna KL. The parathyroid glands, hypercalcemia, and hypocalcemia. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 266.

Update Date: 4/1/2012

Reviewed by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.