The bodies own immune system incorrectly sends out antibodies against Red Blood Cells (RBCs), causing them bind together (Agglutination), then burst and destroy them.

This leads to an insufficient number of Red Blood Cells (Anemic).

Red Blood Cells carry necessary oxygen via the blood from the lungs to muscles and organs.

In this type of Anemia.  The body is working overtime to replace Red Blood Cells (See Retic or Reticulocyte Count).

If Retic is elevated enough to compensate for Hemolysis, then Red Blood Cell counts may stay in a normal range.   For this reason, this disease (CAD) is often missed in its preliminary stages, if a Retic blood test is never performed.  A blood test that is not normal run during any routine annual physical.

See: I was just informed I have Cold Agglutinin Disease – Now what?