Hemosiderin is which form of iron storage?

• A. Soluble iron storage form
• B. Insoluble form of iron storage; occurs when ferritin stores are at capacity
• C. Iron transport protein in plasma
• D. Iron in heme group of hemoglobin

Answer: (B)

Hemosiderin is the insoluble iron-storage complex that forms when ferritin stores are saturated. Ferritin normally holds iron in a soluble, readily mobilizable form for metabolic use. When iron accumulates beyond ferritin’s capacity, ferritin is degraded and iron is sequestered as hemosiderin, an insoluble pigment that accumulates in lysosomes within macrophages. Because it is insoluble, iron in hemosiderin is not as readily mobilized as iron stored in ferritin, which is why hemosiderin is a marker of iron overload or prior bleeding. The iron transport protein in plasma is transferrin, and iron within the heme group of hemoglobin is part of a functional molecule, not storage. The soluble storage form is ferritin, not hemosiderin.