Hemosiderin is a golden-brown pigment made of iron. It forms when the body breaks down red blood cells and stores the iron they contained. Seeing hemosiderin in a tissue sample usually means that bleeding happened in that area at some point in the past.
Hemosiderin is a description of what the pathologist saw under the microscope, not a diagnosis on its own. It is common in skin samples, in areas of old injury, and in some noncancerous tumors. This article explains how hemosiderin forms, what causes it, and what it means in your pathology report.
When blood leaks from a blood vessel into surrounding tissue, red blood cells eventually break down. Immune cells called macrophages move in and swallow the damaged red blood cells. Inside the macrophages, the iron from the red blood cells is packed into small granules of hemosiderin.
This process takes several days. Hemosiderin can then remain in the tissue for months or years. It is the same process that turns a bruise from purple to yellow-brown as it heals.
Under the microscope, hemosiderin appears as golden-brown to dark brown granules. The granules are usually found inside macrophages. Your report may describe these cells as “hemosiderin-laden macrophages” or “siderophages.”
Hemosiderin can look similar to melanin, the brown pigment made by melanocytes in the skin. To tell them apart, the pathologist may use a special iron stain, often called Prussian blue or Perls stain. This stain turns hemosiderin bright blue but does not change melanin’s color.
Hemosiderin builds up wherever red blood cells have leaked out and broken down, or wherever the body is storing extra iron. Common causes include:
A pathologist identifies hemosiderin while examining tissue under the microscope. It is usually recognized by its golden-brown color on routine slides. When the pathologist needs to confirm the pigment, they may use an iron stain.
In a bone marrow biopsy, an iron stain is often done to measure how much iron the body has stored. Low iron stores can support a diagnosis of iron deficiency anemia, while high stores can point to iron overload.
In most cases, hemosiderin indicates old bleeding and is not a concern on its own. It does not mean cancer. Its importance depends on the rest of the report and the reason the sample was taken.
Hemosiderin can also explain why a spot on the skin looked brown or dark. Because a brown spot can sometimes look like a mole or melanoma, finding hemosiderin helps explain the color.