Autoimmune hemolytic anemia
This is what Joey has. I've highlighted parts that particulary pertain to Joey. This information was found at http://www.canismajor.com/dog/autoimmn.html#AHA without consent.
Anemia is a clinical sign, not a disease, and is defined as a decrease in the number of red blood cells (RBCs) or the amount of hemoglobin, resulting in a decrease in the oxygen-carrying capacity of the blood. Anemia can be caused by blood loss, decreased production of new RBCs, or an increase in the rate of their destruction, known as hemolytic anemia.
In hemolytic anemia, the RBCs become "defective" in the eyes of the immune system by acquiring markers on the cell surface that are recognized as "non-self." These markers can be true autoantibodies, as in primary AIHA, or can be secondary to drugs, infectious disease, cancer, blood parasites, or heavy metals. Levamisole, certain antibiotics, Dilantin (phenytoin), lead, and zinc have all been implicated as potential causes of hemolytic anemia.
When the spleen and the rest of the immune system is working to rid the body of old, diseased, or damaged RBCs, it is doing its job appropriately. When a large percentage of cells are affected, and they are removed faster then they can be replaced, AIHA results and the animal shows external signs of the disease.
The clinical signs of AIHA are usually gradual and progressive, but occasionally an apparently healthy pet suddenly collapses in an acute hemolytic crisis. The signs are usually related to lack of oxygen: weakness, lethargy, anorexia, and an increase in the heart rate and respirations. Heart murmurs and pale mucous membranes (gums, eyelids, etc.) may also be present. More severe cases also have a fever and "icterus" (jaundice), a yellow discoloration of the gums, eyes, and skin. This is due to a buildup of bilirubin, one of the breakdown products of hemoglobin.
The diagnosis is usually made on these clinical signs as well as a CBC documenting anemia, often with misshapen or abnormally-clumped RBCs. A Coomb's test may be done to confirm the diagnosis. Corticosteroids are the primary drugs used to treat any autoimmune disease. Very high immunosuppressive doses are used initially to induce a remission, and then the dose is very slowly tapered over many weeks or months to a low maintenance dose. Most affected dogs must be kept on steroids the rest of their lives and are susceptible to relapses.
If steroids alone are insufficient, more potent immunosuppressive drugs such as Cytoxan (cyclophosphamide) or Imuran (azathioprine) may be added. These chemotherapeutics are very effective, but the dog must be monitored closely for side effects, including a decreased white blood count.
Splenectomy, the surgical removal of the spleen, has also been recommended for nonresponsive cases. This benefits the dog in two ways: less antibodies are made against the RBCs, and the primary organ responsible for their destruction is removed. An animal can live quite normally without a spleen.
Blood transfusions are rarely used. Adding foreign protein can actually intensify the crisis state, increase the amount of bilirubin and other breakdown products the liver must process, and suppress the bone marrow's natural response to anemia. In a life-threatening anemia, cross-matched blood may be transfused along with immunosuppressive therapy.