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Fernando Martínez Sáez
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Last update: 01-08-2022

How else can it be called?

  • Anaemia

What is anemia?

Anemia, also called anaemia, is a syndrome defined by a low level of hemoglobin in the blood.

Hemoglobin is the dominant protein of RBCs (Red Blood Cells) that allows transport of oxygen to the tissues. A deficiency of hemoglobin results in a lack of oxygen throughout the body. The amount of hemoglobin necessary for a proper function of the oxygen transport depends on the age, sex, altitude and other circumstances such as pregnancy or smoking.

What are the criteria to diagnose anemia?

WHO (World Health Organization) defines anemia when the hemoglobin concentration in the blood is less than:

Children from 6 month to 6 years old<11 g/dl
Children from 6 to 14 years old<12 g/dl
Men< 13 g/dl
Non-pregnant women< 12 g/dl
Pregnant women< 11 g/dl

Which are the main symptoms of anemia?

Anemia produces a range of symptoms that may vary depending on the cause. Symptoms may include:

  • General symptoms
    • Fatigue.
    • Decreased sexual desire.
    • Dyspnea (shortness of breath).
  • Cardiac symptoms
    • Palpitations.
    • Fatigue after exercise.
    • Hypotension (low blood pressure).
    • Swollen ankles.
  • Neurological symptoms
    • Headache.
    • Dizziness and vertigo.
    • Sleepiness and irritability.
    • Tinnitus (ringing in the ears).
  • Gynecological symptoms
    • Abnormal menstrual bleeding.
  • Skin symptoms
    • Pale skin.
    • Brittle nails.
    • Hair loss.

Besides, in case of severe anemia the following symptoms may be present:

  • Cold skin.
  • Oliguria (low urine output).
  • Painful constriction at the upper part of the belly (angor).

How can anemia be classified according to the size of RBCs (Red Blood Cells)?

Anemia can happen by multiple causes. RBCs size differs depending on the type of anemia. The size of the RBCs is measured by a parameter called MCV (Mean Corpuscular Volume). The MCV allows a classification for the different types of anemia.

  1. Microcytic anemia (MCV < 80 fl)

    RBCs are smaller than usual. It is a feature of the following types of anemia:

  2. Normocytic anemia (MCV between 80 - 100 fl)

    RBCs are relatively normal in size. It can be seen in the following types of anemia:

  3. Macrocytic anemia (VCM > 100 fl)

    There are abnormally large RBCs in size. Macrocytic anemia can be classified as:

Which are the main features of the different types of anemia?

The most common types of anemia, defined by a decreased level of hemoglobin in the blood, are the following ones:

  1. Iron-deficiency anemia

    Iron-deficiency anemia is due to a lack of iron in the body. The lack of iron can be caused by:

    • Loss of blood: Profuse menstrual flow, gastrointestinal bleeding, blood in the urine, etc.
    • Increased need of iron: The body needs more iron in pregnancy, breastfeeding or in the growth stages.
    • Impaired absorption of iron: Bariatric surgery, diarrhea or due to gastrointestinal diseases.
    • Deficient intake of iron in the diet: Low protein diet (e.g., vegetarian diet)
  2. Thalassemia (Hemoglobinopathies)

    Thalassemia is a type of anemia caused by alteration in the synthesis of the hemoglobin. Altered hemoglobin cannot carry enough oxygen to the body cells. It is an inherited disease caused by a genetic disorder.

  3. Anemia of chronic disease

    Anemia of chronic disease is caused by chronic diseases related to the kidneys, digestive system, etc.

  4. Hemolytic anemia

    Hemolytic anemia is caused by a qualitative or intrinsic defect of red blood cells (RBCs). RBCs have normally a biconcave shape. In hemolytic anemias RBCs have a different shape and they are usually destroyed before their normal life span.

    They can be caused by transfusions, toxic substances, etc.

  5. Aplastic anemia

    In aplastic anemia the bone marrow does not produce enough red blood cells (RBCs) or the RBCs produced are immature with an altered function.

  6. Megaloblastic anemia

    Megaloblastic anemia is caused by the lack of folic acid or vitamin B12, two substances required for the production of RBCs.

    The lack of these substances may be due to a deficit in the diet or due to an excessive loss related to gastrointestinal disorders.

When it is considered an emergency?

In case of suffering from anemia it is necessary to visit the doctor. When the anemia is considered an emergency requires an urgent visit to the medical facilities. Sometimes it is not an emergency, but it must be considered by a specialist.

  1. Urgent
    • In case of severe anemia
      • Anemia with cardiovascular alteration.
      • Anemia due to severe bleeding with difficult to stop the hemorrhage or that require transfusion. (Hematocrit<25%; Hemoglobin<7- 8 g/dl).
      • Acute hemolysis crisis (premature destruction of red blood cells).
    • In case of chronic anemia

      Poor clinical or hemodynamic evolution due to exacerbation of the underlying disease (in general hemoglobin below 7-8 g/dl is well tolerated).

  2. Not urgent, but a visit to the specialist is required
    • Microcytic anemia.
      • Sideroblastic anemia.
      • Anemia of chronic disease with unknown origin or not adequate for attention in primary care
    • Normocytic anemia.
      • Hemolytic anemia.
      • Anemia related to bone marrow (where there is more than a blood cell type affected).
      • Anemia of chronic disease with unknown cause or not adequate for attention in primary care.
    • Macrocytic anemia.
      • Megaloblastic anemia to study the underlying causes and prescribe the appropriate treatment.
      • Anemia related to bone marrow (where there is more than a blood cell type affected).
Medically reviewed by our Medical staff on 01-08-2022


  • Harrison’s Hematology and Oncology (3rd Ed) 2017, Dan L. Longo, ISBN: 978-1-25-983582-7, Pag. 10.
  • First Aid for the Basic Sciences: Organ Systems (3rd Ed) 2017, Tao Le, William L. Hwang, Vinayak Muralidhar, Jared A. White and M. Scott Moore, ISBN: 978-1-25-958704-7, Pag. 272.
  • Encyclopedia of Human Nutrition (2nd Ed) 2005, K J Schulze and M L Dreyfuss, ISBN 0-12-150110-8, Vol. I Pag. 101.
  • Anaemia - OMS (World Health Organization) Available on:

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