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Anemia

  1. Anemia can be generally defined as a reduction in hemoglobin level.
    In determining the seriousness of the anemia, the level of hemoglobin is less important than the underlying cause.

    There are three main ways of classifying anemias.
    - Cytometric types: depend on cell size and hemoglobin-content parameters, such as mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC)
    - Erythrokinetic types: take into account the rates of red blood cell (RBC) production and destruction
    - Biochemical/molecular types: consider the cause of the anemia at the molecular level

    The first task in the work-up for a patient with anemia is to classify the case in one of the three major cytometric categories.

    Normocytic, normochromic anemia (normal MCV, normal MCHC)
    - Anemias of chronic disease
    - Hemolytic anemias (characterized by accelerated destruction of RBCs)
    - Anemia of acute hemorrhage
    - Aplastic anemias (characterized by disappearance of RBC precursors from the marrow)

    Microcytic, hypochromic anemia (low MCV, low MCHC)
    - Iron deficiency anemia
    - Thalassemias
    - Anemia of chronic disease (rare)

    Macrocytic, normochromic anemia (high MCV, normal MCHC)
    - Vitamin B12 deficiency
    - Folate deficiency

    The severity of clinical symptoms bears less relationship to the severity of the anemia than to the period of time over which the condition develops.

    An acute hemorrhagic condition may produce symptoms with loss of as little as 20% of the total blood volume (or 20% of the total red cell mass). Conversely, anemias developing over periods long enough to allow compensatory mechanisms to operate will be associated with much greater loss of red cell mass before symptoms are manifested.

    When symptoms do develop, they are related to the precarious state of oxygen delivery to the tissues:
    - Dyspnea on exertion
    - Easy fatigability
    - Fainting, lightheadedness
    - Tinnitus, roaring in the ears
    - Headache
    - Palpitations
    - Exacerbation of pre-existing cardiovascular conditions
    - Angina pectoris, intermittent claudication and nighttime muscle cramps are some of the effects of anemia on already-compromised perfusion.

    Physical findings
    For slowly developing anemia:
    - Pallor
    - Tachycardia
    - Systolic ejection murmur

    In rapidly developing anemia (as from hemorrhage and certain catastrophic hemolytic anemias), additional symptoms and signs are noted:
    - Syncope on rising from bed
    - Orthostatic hypotension (i.e., the blood pressure falls when the patient is raised from a supine to a sitting or standing position)
    - Orthostatic tachycardia

    If anemia develops through rapid bleeding, the hematocrit and hemoglobin will be normal (because in hemorrhage the loss of RBCs and plasma is proportional). Therefore, the appreciation of the clinical signs will be of more value in diagnosing this type of anemia than will the results of laboratory tests.

    Reference: Clinical Practice Guidelines for Nurses in Primary Care. Hematology, Metabolism and Endocrinology. Internet. Accessed August 31, 2009. Available at http://www.hc-sc.gc.ca/fniah-spnia/pubs/services/_nursing-infirm/2000_clin-guide/chap_10a-eng.php#_10-1


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