Calcium, Ionized

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.

What is involved in preparation for the test?

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

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