What is common to all forms of anemia is a reduced number of healthy red blood cells or a decreased ability of the red blood cells to carry oxygen. Anemia itself is a condition characterized by a lower-than-normal level of red blood cells or a decrease in the amount of hemoglobin in the blood, which can result in reduced oxygen delivery to the body's tissues. The specific causes and underlying mechanisms of anemia may vary, but the core characteristic is the impairment of the blood's ability to transport oxygen effectively.