Autoimmune hemolytic anemia

Autoimmune hemolytic anemia refers to increased red blood cell hemolysis, or breakdown, that results when a person’s own antibodies target red blood cells for destruction.

And this results in a lower than normal amount of red blood cells anemia.

The disease is most often idiopathic, or without a known cause, but it can be related to a medication side effect, or an underlying disease process.

Normally, red blood cells, or RBCs, are made in the bone marrow and contain hemoglobin, which is an oxygen binding protein that delivers oxygen to tissues.

Red blood cells live about 100-120 days after which they are recycled in the bone marrow or consumed by macrophages in the spleen, liver, or lymphatic system.

Now, autoimmune hemolytic anemia is an extrinsic type of hemolytic anemia, because the immune system mistakenly believes our own red blood cells are foreign, or non-self, structures, so it secretes antibodies against proteins found on the RBC membrane.

If there had been a primary defect in the RBC membrane, then it would have been called an intrinsic hemolytic anemia.

And usually, hemolysis happens in the spleen or liver, so this is considered an extravascular hemolytic anemia - although in severe cases, RBC hemolysis can also happen intravascularly, or inside blood vessels.

Now, autoimmune hemolytic anemia gets classified as either warm or cold.

Warm is the more common type, and it’s when hemolysis occurs at temperatures greater than or equal to core human body temperature of 37º celsius.

Cold autoimmune hemolytic anemia is much rarer, and it occurs when people’s blood is exposed to cold temperatures, usually in the range of 0º to 10º celsius - like when a person goes out into cold weather during winter.

Warm autoimmune hemolytic anemia is almost always due to IgG antibodies, termed “warm agglutinins” that react with antigens, which are proteins on the surface of the red blood cell.

The main red blood cell antigen that reacts with these IgG antibodies is the Rh antigen.

When these antibodies bind to the antigen on the RBC membrane, they bind to the surface of the red blood cell and trigger a process called antibody-dependent cell mediated cytotoxicity.

In this reaction, immune cells including macrophages, neutrophils, natural killer cells, or CD8+ T-cells bind to the Fc portion of the antibody via a cell membrane receptor called the Fc receptor.