Polycythemia and erythrocytosis

Discussion in 'Step I' started by cbrons, 09.22.14.

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  1. cbrons

    cbrons love machine Bronze Donor 7+ Year Member

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    What do you think of my definition of polycythemia?

    Polycythemia: Abnormally high red cell count as determined by an above-normal hemoglobin and/or hemocrit level.

    See the problem I am having is that Harrison's, Robbins & Cotran, and Williams Hematology all define polycythemia in different ways.

    Williams Hematology, 8e: "Polycythemia is characterized by an increased red cell volume."

    Harrison's Internal Medicine, 18e: "Polycythemia is defined as an increase in the hemoglobin above normal."

    Robbins and Cotran, 9e: "Polycythemia denotes an abnormally high red cell count, usually with a corresponding increase in the hemoglobin level."

    Further complicating the matter is that in many resources, "erythrocytosis" is the preferred term for any increase in red cell mass, while "polycythemia" implies not only increased hemoglobin and hematocrit levels but also leukocytosis and thrombocytosis.

    I'm really only concerned with a solid operating definition insofar as Step I is concerned, and First Aid says that "polycythemia = erythocytosis = increased hematocrit"
     
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  3. Transposony

    Transposony Do or do not, There is no try 5+ Year Member

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    They are all saying the same thing which FA has put quite succinctly.
     
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  4. Brain Bucket

    Brain Bucket Oh man, I forgot to bring the marshmallows. 2+ Year Member

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    Break down the words...polycythemia is not limited to RBCs, whereas erythrocytosis is just the numerical increase in circulating RBCs.

    Oddly enough, Robbins seems to have the best definition, but I'm just a MS-3, wtf do I know?

    Don't get caught up in this stuff.
     
  5. DeeJay2728

    DeeJay2728 5+ Year Member

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    For example, Polycythemia Vera there is mainly an increase in RBCs but there is also an increase of other cell types, which is why the patient commonly presents with itching after a hot bath (increased number of granulocytes... Increased degranulation)
     
  6. cbrons

    cbrons love machine Bronze Donor 7+ Year Member

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    I hear you but the term "polycythemia" seems to imply an leukocytosis and thrombocytosis as well, whereas "erythrocytosis" is only an increase in red cell mass
     
  7. animando

    animando 2+ Year Member

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    The word polycythemia indicates increased red blood cells, white blood cells, and platelets. Most of the time, it is used in place of erythrocythemia, or pure red blood cell increase, such as in secondary polycythemia.
    The term polycythemia is reserved for the myeloproliferative disorder calledpolycythemia vera, in which all 3 peripheral blood cell lines can be increased.
    Erythrocytosis or erythrocythemia is a more specific term that is used to denote increased red blood cells.

    http://emedicine.medscape.com/article/205039-overview

    By the way I personally think this is a pointless detail.
     
  8. IH8ColdWeath3r

    IH8ColdWeath3r 5+ Year Member

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    The way I think about it is...

    Polycythemia = increased Hb, Hct, RBC mass

    there are different kinds of polycythemia, those that are appropriate (triggered by a hypoxic stimulus) vs inappropriate (not triggered by a hypoxic stimulus, like ectopic EPO production)--in either case, you have an increase in RBC mass, which is due to the increase in the number of RBC's (and thus increased Hb, Hct, and RBC mass)

    RELATIVE polycythemia, on the other hand, is an increase in RBC mass but this time it is due to dehydration or fluid loss from say (sweating, exercise, burn)...so the increase in RBC mass is RELATIVE to plasma volume. Thus, is not a true increase in RBC mass due to production, but rather due to a depletion of plasma volume, so RBC mass, and thus, Hct, is elevated with respect to the decrease in plasma volume

    Lastly, Polycythemia Vera (PV), is a myeloproliferative disorder characterized by a an increase in all cells that come from the myeloid lineage, and so, while you have an increase in granulocytes, monocytes, megakaryocytes, platelets, and erythrocytes---the increase in erythrocytes (and thus, Hb, Hct, and RBC mass) as the predominant cell type in this disorder is designated by the name.

    What you'll notice is that in each case, the increase RBC mass is accounted for by the word polycythemia. These conditions all differ, but, from this distinctions above, one can see that the simplest way of understanding it is polycythemia = increased RBC mass

    Don't get caught up on the little details like this though..it will make going through FA more difficult than it already is
     

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