A ferritin test measures the amount of ferritin in the blood. Ferritin is a blood protein that contains iron. This test can be used to find out how much iron the body stores.

If a ferritin test shows that the blood ferritin level is low, it means the body’s iron stores are low. This is a condition called iron deficiency. Iron deficiency can cause anemia.

If a ferritin test shows high ferritin levels, it most often means swelling in the body, called inflammation. Conditions that can cause inflammation include liver disease, rheumatoid arthritis and other inflammatory conditions, and overactive thyroid, called hyperthyroidism. Rarely, a high ferritin level could be from a condition that causes the body to store too much iron. Some types of cancer also can cause the blood ferritin level to be high.