Anemia is a pathologic deficiency in the amount of oxygen-carrying hemoglobin in the red blood cells. It can result from a failure of red-blood-cell or hemoglobin production. When anemia results from another disease, it is referred to as symptomatic or secondary anemia. Some common causes of symptomatic anemia are cancer, kidney disease and autoimmune disorders.

There are more than 400 different types of anemia. Their causes can be divided into three categories: 1) anemia caused by blood loss; 2) anemia caused by decreased or faulty red-blood-cell production; 3) anemia caused by destruction of red blood cells.

Anemia symptoms include fatigue, fainting, shortness of breath and palpitations. Patients may also appear pale. In cases of anemia due to stomach or intestinal bleeding, the stool may appear black or bloody.

Cancers, particularly those of the bone marrow, can alter the production of blood cells and produce anemia. This can result from the cancer cells using available nutrients and resources to grow or from cancer medications that inhibit replication of normal bone marrow cells in addition to cancer cells.

Healthy kidneys make erythropoietin, which stimulates the bone marrow to produce blood cells. Kidney disease can result in decreased erythropoietin production, which then reduces blood cell production, resulting in anemia.

Iodine deficiency is the foremost cause of hypothyroidism. In countries where iodine intake is inadequate, autoimmune thyroid disease is most common. One third of patients with hypothyroidism develop anemia, with decreased red-blood-cell mass and erythropoietin resistance. The cause for this association is unclear, but it may be due to mineral interactions or autoimmune antibodies.

Autoimmune hemolytic anemia occurs when the immune system attacks the red blood cells, leading to their destruction (hemolysis). Drugs such as methyldopa and fludarabine can cause this condition.

There are several treatments available, depending on the underlying cause of the anemia. Nutritional treatments include iron and vitamin B-12 or folic acid. Other treatments focus on the primary disease in an effort to eliminate autoimmunity, infections, inflammation, or malignancies. Erythropoietin may also be given to stimulate blood cell production. In the event that blood cell counts are dangerously low or fail to respond to treatment, blood transfusions may also be given.