Evidence for multiple causes appears with an elevated RBC distribution width (RDW), indicating a wider-than-normal range of red cell sizes, also seen in common nutritional anemia. Heinz body anemia
Heinz bodies form in the cytoplasm of RBCs and appear as small dark dots under the microscope. In animals, Heinz body anemia has many causes. It may be drug-induced, for example in cats and dogs by acetaminophen (paracetamol), or may be caused by eating various plants or other substances:

In cats and dogs after eating either raw or cooked plants from the genus Allium, for example, onions or garlic. In dogs after ingestion of zinc, for example, after eating U.S. pennies minted after 1982. In horses which eat dry or wilted red maple leaves. Hyperanemia
Hyperanemia is a severe form of anemia, in which the hematocrit is below 10%. Refractory anemia
Refractory anemia, an anemia which does not respond to treatment, is often seen secondary to myelodysplastic syndromes. Iron deficiency anemia may also be refractory as a manifestation of gastrointestinal problems which disrupt iron absorption or cause occult bleeding. Transfusion dependent
Transfusion dependent anemia is a form of anemia where ongoing blood transfusion are required. Most people with myelodysplastic syndrome develop this state at some point in time. Beta thalassemia may also result in transfusion dependence. Concerns from repeated blood transfusions include iron overload. This iron overload may require chelation therapy. Treatment
Treatment for anemia depends on cause and severity. Vitamin supplements given orally (folic acid or vitamin B12) or intramuscularly (vitamin B12) will replace specific deficiencies.
In the United States, 12% of all women of childbearing age have iron deficiency, compared with only 2% of adult men. The incidence is as high as 20% among African American and Mexican American women. Studies have shown iron deficiency without anemia causes poor school performance and lower IQ in teenage girls, although this may be due to socioeconomic factors. Iron deficiency is the most prevalent deficiency state on a worldwide basis. It is sometimes the cause of abnormal fissuring of the angular (corner) sections of the lips (angular stomatitis). In the United States, the most common cause of iron deficiency is bleeding or blood loss, usually from the gastrointestinal tract. Fecal occult blood testing, upper endoscopy and lower endoscopy should be performed to identify bleeding lesions. In older men and women, the chances are higher that bleeding from the gastrointestinal tract could be due to colon polyps or colorectal cancer. Worldwide, the most common cause of iron deficiency anemia is parasitic infestation (hookworms, amebiasis, schistosomiasis and whipworms).The Mentzer index (mean cell volume divided by the RBC count) predicts whether microcytic anemia may be due to iron deficiency or thalassemia, although it requires confirmation. Macrocytic
Megaloblastic anemia, the most common cause of macrocytic anemia, is due to a deficiency of either vitamin B12, folic acid, or both. Deficiency in folate or vitamin B12 can be due either to inadequate intake or insufficient absorption. Folate deficiency normally does not produce neurological symptoms, while B12 deficiency does.