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Anemia Definition Symptoms and Causes

The anemia is a relatively common condition that is characterized by a lack of red blood cells . Red cells are cells found in the blood. They serve, among other things, to bring oxygen to tissues and organs.

People with anemia may feel tired and run out of breath more easily than usual because their heart has to work harder to supply their body with oxygen.

According to the World Health Organization , 25% of the world population suffers from anemia 1. Half of these cases is due to a deficiency of nutrition in iron . The women who have heavy periods, the children of preschool age and pregnant women are most at risk of anemia.

Causes of Anemia 

Several situations can lead to anemia.

  •  An iron deficiency.
  • A deficiency of vitamins.
  • A chronic disease or a disease of the bone marrow.
  • A genetic disease , which causes for example too rapid destruction of red blood cells.
  • A bleeding , that is to say a flow of blood outside the blood vessels.

Red blood cells, iron and hemoglobin

Red blood cells are blood cells consisting essentially of hemoglobin . Hemoglobin is composed of a protein (globin) and a pigment (heme). It is the latter which gives the blood red color. It fixes iron that carries oxygen from the lungs to the cells. Oxygen is needed to produce energy in cells and allows the organs to perform their functions. The pigment bound to oxygen takes on a reddish-red color and circulates in the arteries . Hemoglobin also carries carbon dioxide (waste from the combustion of oxygen) from the cells to the lungs. It then becomes purplish red and circulates in the veins .

Main types of anemia

Iron deficiency anemia . This is the most common form of anemia. Abundant menstruation and low iron diet are the most frequent causes. Iron deficiency anemia modifies the size of red blood cells, which become smaller than normal (microcytic anemia). For more information, see our Anemia Iron Sheet.

Anemia caused by vitamin deficiency . This type of anemia produces deformed and very large red blood cells (macrocytic anemia). The most common are those caused by vitamin B12 deficiency or vitamin B9 (folic acid). The first can occur due to insufficient dietary intake of this vitamin, its poor absorption in the intestine or a disease called pernicious anemia. For more details, see our B12 Deficiency Anemia Fact Sheet .

Anemia caused by a chronic disease. Many chronic diseases (and sometimes their treatments) can reduce the amount of circulating red blood cells in the blood. This is the case of cancer, Crohn’s disease and inflammatory diseases such as rheumatoid arthritis. Renal insufficiency can also cause anemia, as the kidneys secrete erythropoietin, the hormone that stimulates the production of red blood cells. However, they retain their normal size and appearance (normocytic anemia).

Hemorrhagic anemia . Significant blood loss after a serious accident, surgery or childbirth, for example, can quickly lead to anemia. Some gastrointestinal problems (peptic ulcer, intestinal polyps or colorectal cancer) can also lead to it, but this time by causing a slight and steady loss of blood in the stool (sometimes invisible) over a long period of time.

Hemolytic anemia . This type of anemia is characterized by too rapid destruction of the red blood cells. It may be due to a reaction of the immune system ( autoimmune or allergic), presence of toxins in the blood, infections (eg malaria), or congenital (sickle cell anemia, thalassemia, etc.). The congenital form mainly affects individuals of African descent.

Sideroblastic anemia . This term encompasses a group of very rare anemias in which red blood cells can not fix iron in hemoglobin . It is an enzymatic problem of hereditary or acquired origin. Red blood cells are smaller than normal.

Aplastic (or aplastic) anemia. This rare disease occurs when the bone marrow no longer produces enough blood stem cells. Thus, there is not only a lack of red blood cells, but also of white blood cells and platelets. In 50% of cases, aplastic anemia is caused by toxic agents, certain drugs or exposure to radiation. It can also be explained by serious diseases, such as bone marrow cancer (for example, leukemia).


Since it is not possible to rely solely on symptoms for diagnosis , it is necessary to undertake a laboratory examination of a blood sample . A hemogram (complete blood count) is normally prescribed by the doctor.


Here are the 3 main parameters  :


Hemoglobin  : the concentration of hemoglobin (the red blood cell respiratory pigment) in blood, expressed in grams of hemoglobin per liter of blood (g / l) or per 100 ml of blood (g / 100 ml or g / dl).

Hematocrit  ratio: The ratio, expressed as a percentage, of the volume of red blood cells in a blood sample (passed to the centrifuge) relative to the total blood volume in that sample.

Red blood cell count  : the number of red blood cells contained in a given blood volume, normally expressed in millions of red blood cells per microliter of blood (million / μl).



Note. These values ​​of hemoglobin and hematocrit correspond to the norm for 95% of people. This means that 5% of individuals have “non-standard” values ​​while being healthy. On the other hand, results at the lower end of normal may reflect an onset of anemia if they were usually higher.


Other blood tests may be required to clarify a diagnosis and discover the cause of anemia. Depending on the case, the size of the red blood cells, the determination of iron or different vitamins in the blood, etc. can be carried out.

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