What is an Iron Blood Test?

Medically Reviewed by Sabrina Felson, MD on December 16, 2022
2 min read

Iron is a mineral in your body that comes from foods like red meat and fortified cereals or from supplements you take. You need iron to make red blood cells. Iron is also an important part of hemoglobin, a protein in your blood that helps carry oxygen from your lungs to the rest of your body.

An iron test can show if you have too much or too little of this mineral in your system. It can check for conditions like anemia, or iron overload (excess iron). Your doctor might order a test if you have symptoms of either condition.

Symptoms of low iron include:

Symptoms of high iron include:

There are several different tests to check the level of iron in your body. These tests show how much of the mineral is moving through your blood, how well your blood carries it, and how much iron is stored in your tissues.

  • Serum iron. This test measures the amount of iron in your blood.
  • Serum ferritin. This test measures how much iron is stored in your body. When your iron level is low, your body will pull iron out of “storage” to use.
  • Total iron-binding capacity (TIBC). This test tells how much transferrin (a protein) is free to carry iron through your blood. If your TIBC level is high, it means more transferrin is free because you have low iron.
  • Unsaturated iron-binding capacity (UIBC). This test measures how much transferrin isn’t attached to iron.
  • Transferrin saturation. This test measures the percentage of transferrin that is attached to iron.

Some tests require you to stop eating about 12 hours before you give blood. Your health care provider will take a sample from a vein in your arm and send it to a lab. The lab results will show whether iron levels in your blood are too high or too low.

A low iron level can be caused by:

  • A lack of iron in your diet
  • Trouble absorbing iron from foods you eat
  • Blood loss
  • Pregnancy

A lack of iron can affect your body's ability to make red blood cells. If your iron level is too low, you could have anemia. This means you don't have enough healthy red blood cells to transport oxygen to your organs and tissues.

A high iron level can be caused by:

Talk to your doctor about the meaning of your test results. Find out what steps to take to treat your condition.