Anemia (often called "low blood" by the public) is the condition where there is a low level of hemoglobin in the red cells. Hemoglobin is responsible for carrying oxygen throughout the body and a person with low hemoglobin may feel unusually tired because of inadequate oxygen delivery.

There are two main reasons why someone may be anemic:

• inadequate production of red blood cells
• loss of blood.

There are close to 100 different conditions that lead to anemia. The most common cause worldwide is iron deficiency. Iron is an essential component of hemoglobin. Insufficient iron in the diet will prevent the body from producing a normal amount of hemoglobin. This is very important in children and menstruating or pregnant women because their requirement for iron is high. Another cause of anemia is the loss of iron because of chronic bleeding. The most common reason for losing blood is monthly menstrual bleeding. Another, cause is bleeding into the intestine from a stomach ulcer or bowel cancer.

Another common reason for anemia is a chronic disorder such as Rheumatoid arthritis or kidney failure in which the production of red cells is impaired.

The first step in making an anemia diagnosis is to measure the amount of hemoglobin and to count the red blood cells and examine their size and shape. This is accomplished with the Hematology Profile. This is performed using a large, automated analyzer and may be supplemented by examining the cells with a microscope.

Another common anemia test is the measurement of serum Ferritin or serum Iron. Ferritin is now the preferred test for the measurement of iron deficiency. Ferritin is a molecule that stores iron in the body. Low Ferritin indicates low iron storage levels and having low iron stores is a very high-risk situation for anemia.

Other causes of anemia may require a sequence of different tests, each one leading to more information. Some of these tests are: Vitamin B12, Folate, and special hemoglobin studies.  Thus, the diagnosis of anemia usually starts out with common tests but may need to carry on with a whole series of more complex procedures.