Polychromasia
| Polychromasia | |
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| Reticulocytes Human Blood Supravital Stain | |
| Classification and external resources | |
| MedlinePlus | 001318 |
Polychromasia (also known as Polychromatophilia) is a disorder where there is an abnormally high number of immature red blood cells found in the bloodstream as a result of being prematurely released from the bone marrow during blood formation.(Poly- refers to many, and -chromasia means color.) These cells are often shades of grayish blue. Polychromasia is usually a sign of bone marrow stress as well as immature red blood cells. 3 types are recognized, with types (1) and (2) being referred to as 'young red blood cells' and type (3) as 'old red blood cells'. Giemsa stain is used to distinguish all three types in blood smears. The young cells will generally stain gray or blue in the cytoplasm. These young red blood cells are commonly called reticulocytes. All polychromatophilic cells are reticulocytes, however, not all reticulocytes are polychromatophilic. In the old blood cells, the cytoplasm either stains a light orange or does not stain at all.
The formation of red blood cells is commonly known as haematopoiesis. Up to the first 60 days of life, the yolk sac is the main source of haematopoiesis. The liver is then used as the main hematopoietic organ of the embryo until near birth, where it is then taken over by the bone marrow. Most red blood cells are released into the blood as reticulocytes. Polychromasia occurs when the immature reticulocytes of the bone marrow are released, resulting in a grayish blue color of the cells. This color is seen because of the ribosomes still left on the immature blood cells, which are not found on mature red blood cells. These cells still contain a nucleus as well due to the early release, which is not needed in mature blood cells because their only function is to carry oxygen in the blood. The life span of a typical red blood cell is acknowledged to be approximately 120 days and the time period of a reticulocyte found in the blood to be one day. The percentage of reticulocytes calculated to be in the blood at any given time indicates the rapidity of the red blood cell turnover in a healthy patient. The number of reticulocytes, however, reflects the amount of erythropoiesis that has occurred on any certain day. The absolute number of reticulocytes is referred to as the reticulocyte index and is calculated by adjusting the reticulocyte percentage by the ratio of observed hematocrit to expected hematocrit to get the 'corrected' reticulocyte count.
Red blood cells can be released prematurely by a number of mechanisms. Premature release of red blood cells is usually caused due to damage of the bone marrow due to underlying causes as well as in response to the stimulation of hormones in strong association with anemia. Erythropoetin, a hormone made by the kidneys, controls the production of the red blood cells as well as the rate at which they are released from the bone marrow. When these levels of erythropoetin rise, they signal the release of immature red blood cells into the bloodstream and is linked to anemia. Damaged bone marrow can also lead to polychromasia. The most common cause of bone marrow damage is penetration by cancer cells, either from the bone marrow itself or as a consequence of metastasis from another part of the body.
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