Calcium, Ionized

Overview & Description

This test measures the levels of free calcium in the blood.

Free calcium, or calcium not bound to blood proteins, is themetabolically active form of calcium. Metabolically active calcium is available for use by the cells.

Who is a candidate for the test?

This test may be ordered to help diagnose disorders of the bones, parathyroid gland, and some forms of cancer. It can also help diagnose nutritional deficiencies.

How is the test performed?

A blood sample is taken from a vein on the forearm or hand so that the amount of free calcium in the blood can be measured. To take the blood, a technician first cleans the skin over the vein with an antiseptic. Next, he or she wraps a strong rubber tube, or tourniquet, around the upper arm. This restricts blood flow through the veins in the lower arm and causes them to enlarge. The technician gently inserts a small needle into a vein and removes the tourniquet. Blood flows from the vein through the needle and is collected in a syringe or vial. After withdrawing the needle, the technician covers the puncture site to prevent bleeding. The sample is sent to a laboratory for testing.

Preparation & Expectations

What is involved in preparation for the test?

A person should ask his or her healthcare provider for specific instructions for taking this test.

Results and Values

What do the test results mean?

The normal range for levels of free calcium in the blood is from 4.4 to 5.3 milligrams per deciliter (mg/dl) in adults and from 4.4 to 6.0 mg/dl in children.

Abnormally high levels of free calcium may indicate:

  • hyperparathyroidism, or excess activity of the parathyroid glands
  • metastatic bone tumor, or cancer cells are spreading to other parts of the body from a tumor in the bone
  • milk-alkali syndrome, which occurs when continuous ingestion of antacids has caused loss of normal body acidity
  • multiple myeloma, a cancer of the bone marrow
  • Paget’s disease, a bone disorder causing deformities
  • sarcoidosis, a disorder causing abnormalities of the bones, lungs, skin, eyes, muscles and lymph nodes
  • tumors producing molecules that mimic the activity of the parathyroid glands
  • vitamin D intoxication
  • Abnormally low levels of free calcium may indicate:

  • hypoparathyroidism, or abnormally low activity of the parathyroid glands
  • malabsorption of nutrients from the bowel
  • osteomalacia, or bone softening in adults
  • pancreatitis, or inflammation of the pancreas
  • kidney failure
  • rickets, or bone softening in children
  • vitamin D deficiency
  • Article type: xmedgeneral