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

Free calcium, or calcium not bound to blood proteins, is the metabolically 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.