A ferritin blood test measures the amount of ferritin, a protein that stores iron in your body. This test helps doctors understand how much iron is stored in your body. You might need this test if you have symptoms of low or high iron levels, such as fatigue, weakness, or joint pain. The test can also help diagnose conditions like anemia or hemochromatosis. To perform the test, a lab technician will clean the skin on your arm, insert a needle into a vein, and draw a small amount of blood. The procedure is quick and safe, and you can usually eat and drink normally before the test unless instructed otherwise by your doctor.