Ferritin is a protein that acts as the main storage for iron inside the cells. The Ferritin Test checks for the levels of ferritin in blood to determine the levels of iron in the body and judge the body's capacity to store iron. Serum ferritin is a blood test commonly performed independently or as part of an iron profile test. Ferritin is a protein found in the blood. Its levels help to estimate the levels of iron in the body. It is also an acute-phase reactant produced during inflammation.