What are ring sideroblasts?

Ring sideroblasts are immature red blood cells (cells that are still developing in the bone marrow) that contain too much iron. Instead of being stored in the normal location, the iron builds up inside the developing red blood cell and forms a ring-shaped pattern around the nucleus, which is the control center of the cell.

Pathologists see ring sideroblasts when they examine bone marrow samples under a microscope using a special stain that highlights iron. These cells are abnormal and usually appear when the body has trouble using iron properly to make healthy red blood cells.

How do ring sideroblasts develop?

To understand ring sideroblasts, it helps to know how red blood cells are normally made. Red blood cells are produced in the bone marrow, and iron is a key ingredient because it is needed to make hemoglobin, the protein that carries oxygen throughout the body.

In healthy cells, small amounts of iron are used to build hemoglobin, and any extra iron is stored safely. In ring sideroblasts, however, the developing red blood cell cannot process iron properly. As a result, the iron collects in a circle around the nucleus instead of being used or stored normally.

This abnormal iron buildup is what gives ring sideroblasts their name and appearance.

Where is iron normally stored in the body?

Iron is essential for making new red blood cells, but the body must store it carefully so it can be released when needed.

Normal iron storage includes:

• Macrophages in the bone marrow: These specialized immune cells act as iron “warehouses.” They hold iron until developing red blood cells need it.

• Immature red blood cells: A small amount of iron is held temporarily inside these cells while they are making hemoglobin. Pathologists can see this iron as tiny granules (small dots) inside the cell under the microscope. In healthy cells, only a few granules are present.

When ring sideroblasts are present, the iron granules are numerous and arranged in a complete or nearly complete ring around the nucleus instead of being scattered normally.

What conditions can cause ring sideroblasts?

Ring sideroblasts can be seen in several medical conditions. Some are reversible and related to nutrient deficiencies or medications, while others are due to bone marrow disorders. Common causes include:

Myelodysplastic syndromes (MDS)

MDS is a group of disorders in which the bone marrow does not produce blood cells properly. A specific type of MDS, once called MDS with ring sideroblasts, shows a high number of these abnormal cells.

Nutritional deficiencies

• Copper deficiency can interfere with the body’s ability to use iron, leading to ring sideroblasts.

• Vitamin B6 deficiency is another rare cause because B6 is needed for hemoglobin production.

Inherited conditions

Some rare genetic disorders, such as X-linked sideroblastic anemia, cause the bone marrow to form ring sideroblasts from birth or early childhood.

Medications and toxins

Certain medications and toxins interfere with iron processing in the bone marrow. Examples include:

• Some antibiotics and chemotherapy drugs.

• Excessive alcohol use.

• Lead poisoning.

When the cause is reversible, treating the underlying condition may help reduce the number of ring sideroblasts.

How do pathologists identify ring sideroblasts?

Ring sideroblasts are easiest to see using an iron stain (often called a Prussian blue stain), which highlights iron deposits in bright blue. Under the microscope, pathologists look for:

• A ring of 10 or more granules.

• Surrounding one-third or more of the nucleus.

• Within an immature red blood cell (erythroblast).

Only cells with this specific pattern are called ring sideroblasts. Cells with a few scattered granules are considered normal.

Why are ring sideroblasts important?

Finding ring sideroblasts in a bone marrow biopsy can help doctors:

• Identify the cause of anemia (low red blood cell count).

• Diagnose or classify myelodysplastic syndromes.

• Detect nutritional deficiencies.

• Recognize possible medication-related side effects.

• Guide testing for inherited blood disorders.

Seeing ring sideroblasts does not mean a person has cancer. Instead, it means the bone marrow is having trouble using iron correctly, and further testing may be needed to find the cause.

Questions to ask your doctor

• What caused the ring sideroblasts in my bone marrow sample?

• Do I need additional tests to look for nutritional deficiencies or genetic conditions?

• Could a medication or toxin be contributing to this finding?

• Do I have a form of myelodysplastic syndrome?

• What treatments are available for my condition?

• Will my bone marrow need to be rechecked in the future?