What are the consequences of leaving anemia untreated?

Untreated anemia: Bad anemia can cause fatigue, lightheadedness, chest pain, shortness of breath, and leg pain with exercise. Some cases require blood transfusion. There are literally hundreds of causes of anemia, many of which are easily treatable, and others which are mild or congenital and don't need treatment at all. To find out what kind of anemia someone has and whether it needs treatment, see a hematologist.