There are two forms of IMHA: primary (or idiopathic), and secondary IMHA. With primary IMHA, your dog's immune system mistakenly produces antibodies that attack its own red blood cells. This is the most common cause of anemia in dogs.With secondary IMHA, the surface of your dog’s red blood cells is modified by an underlying disease process, drug, or toxin. Your dog's immune system identifies the modified red blood cells as something foreign and destroys them.nemia is a condition that arises when the number of red blood cells falls below normal values, or the red blood cells function improperly. There are many diseases and conditions that can cause anemia in dogs.