Hemosiderin: Definition

Print this article

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.

How does hemosiderin form?

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.

What does hemosiderin look like under the microscope?

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.

What causes hemosiderin in tissue?

Hemosiderin builds up wherever red blood cells have leaked out and broken down, or wherever the body is storing extra iron. Common causes include:

Past injury or bleeding. Any area that has bled in the past, such as a bruise, a surgical site, or a scar, may contain hemosiderin.
Poor blood flow in the legs. When blood pools in the veins of the lower legs, small amounts leak into the skin. Over time, hemosiderin builds up, and the skin turns brown.
Some noncancerous tumors. Growths such as a dermatofibroma and giant cell tumor of the tendon sheath often contain hemosiderin.
Blood vessel tumors. Tumors made of blood vessels, such as a hemangioma or Kaposi sarcoma, often leak blood and contain hemosiderin.
Too much iron in the body. In conditions where the body stores too much iron, such as after many blood transfusions, hemosiderin can build up in organs such as the liver.

How is hemosiderin identified?

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.

What does hemosiderin mean for me?

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.

Questions to ask your doctor

What caused the hemosiderin in my sample?
Does the hemosiderin mean there was bleeding in this area?
Is the hemosiderin related to my diagnosis?
Was an iron stain done, and what did it show?
Does this finding explain the brown color of my skin spot?
Does this finding suggest a problem with the amount of iron in my body?
Do I need any further tests or follow-up?