hemosiderine

Hemosiderine (also spelled haemosiderin or hemosiderine) is an iron-containing, brownish granular pigment that accumulates in tissues following the breakdown of hemoglobin. It is not a discrete molecule but an aggregate of partially degraded ferritin, denatured proteins, and iron, typically found within lysosomes of macrophages and other cells involved in phagocytosis.

Formation of hemosiderine occurs when excess iron released from hemoglobin after hemorrhage or red blood cell degradation overwhelms normal storage pathways. Ferritin molecules aggregate and undergo partial proteolysis, producing the less-soluble hemosiderine complex. Because iron in hemosiderine is less readily mobilized than iron stored as ferritin, its presence indicates localized or systemic iron sequestration.

Clinically, detection of hemosiderine serves as a marker of prior or ongoing bleeding and chronic iron overload. It is commonly seen in conditions such as chronic venous stasis, repeated hemorrhage in tissues, pulmonary hemosiderosis, and after multiple blood transfusions. Histologically, the pigment is demonstrated by Prussian blue (Perls’) stain, which highlights ferric iron.

While hemosiderine deposition signals altered iron handling and tissue injury, management focuses on addressing underlying causes of hemorrhage or iron overload. In systemic iron excess, therapeutic measures may include phlebotomy or chelation under medical supervision; focal tissue deposits may resolve slowly as macrophages clear iron when bleeding stops.