What is Hemosiderin?

You have heard the term hemosiderin, and you have probably ordered a urine hemosiderin test in a patient with suspected hemolytic anemia and hemoglobinuria. But what is it exactly? And how does it relate to iron and ferritin?

• There are two storage forms of iron are known in animals:
  • Ferritin
  • Hemosiderin
• Both are present in virtually all cells/tissues but occur principally in liver, spleen, and bone marrow.
• Both contain the ferric form of iron (Fe³⁺).
• Ferritin degradation in lysosomes gives rise to hemosiderin.
• Hemosiderin consists of aggregates of insoluble, denatured ferritin molecules from which much of the protein shell has been removed by proteolytic digestion.¹²
• Tissue staining with Perls Prussian blue is able to detect hemosiderin (shows a punctate pattern of staining), but not ferritin.³
• While the normal pathway for iron storage flows from ferritin to hemosiderin:
  • Hemosiderin can form through ferritin-independent pathways (when the rate of uptake of iron exceeds the tissue’s capacity to make ferritin protein).
  • Hemosiderin-associated iron can recycle back to ferritin (albeit inefficiently).⁴