Serum iron is a test that measures how much iron is in your blood.

Your doctor may order this test if you have signs of low iron (iron deficiency).

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

Iron levels are highest in the morning. It's best to do this test in the morning, if a deficiency is suspected.

Make sure your doctor knows about all the medications your are taking.

Drugs that can increase iron include estrogens, birth control pills, and methyldopa.

Drugs that can lower iron include cholestyramine, colchicine, deferoxamine, methicillin, allopurinol, and testosterone.

When the needle is inserted to draw blood, some people feel moderate pain. Others will feel only a prick or stinging sensation. Afterward, there may be some throbbing.