It may serve other functions as well although these are controversial. It is found in most cells of the body, especially macrophages, hepatocytes and erythrocytes.
Synthesis occurs in the liver and the rate correlates directly with the cellular iron content.
Sensitive methods are needed, since serum levels are very low. Canine and feline-specific ferritin assays are available through Kansas University. A decrease in the amount of stored iron is the only known cause for a low serum ferritin result. This is the strong point of this test. However, in dogs, serum ferritin values do not appear to correlate with bone marrow iron stores, and normal ferritin values may be seen in dogs with documented iron deficiency.