Iron-deficiency anemia is anemia caused by a lack of iron. Anemia is defined as a decrease in the number of red blood cells or the amount of hemoglobin in the blood. When onset is slow, symptoms are often vague including feeling tired, weakness, shortness of breath, or poor ability to exercise. Anemia that comes on quickly often has greater symptoms including: confusion, feeling like one is going to pass out, and increased thirst. There needs to be significant anemia before a person becomes noticeably pale. Problems with growth and development may occur in children. There may be additional symptoms depending on the underlying cause. Iron-deficiency anemia is usually caused by blood loss, insufficient dietary intake, or poor absorption of iron from food. Sources of blood loss can include heavy periods, childbirth, uterine fibroids, stomach ulcers, colon cancer, and urinary tract bleeding. A poor ability to absorb iron may occur as a result of Crohn's disease or a gastric bypass. In the developing world parasitic worms, malaria, and HIV/AIDS increase the risk. Diagnosis is generally confirmed by blood tests.