Erythroblastemia: Description, Causes and Risk Factors:Anemia characterized by the presence of large numbers of nucleated red cells (normoblasts and erythroblasts) in the peripheral blood. Seen in newborns with hemolytic anemia, due to isoimmunization, such as that caused by Rh or ABO incompatibility.The term erythroblastemia describes the presence of nucleated red cells in circulating blood. Erythroblasts are not found in the blood of healthy persons in whom the increased demand for red cells is met by an orderly delivery of reticulocytes into circulation. Thus, erythroblastemia indicates an underlying disorder. An exception is the newborn infant in whom a few nucleated red cells may normally be present in blood during the first week. Prematurity, anemia or obstetrical complications resulting in antenatal hypoxia, may intensify this otherwise normal finding. Presumably, erythroblastemia in the normal neonate results from a lack of maturity of those mechanisms that serve to keep these cells out of circulation.Erythroblastemia is seen in association with a variety of hematologic and non-hematologic disorders and indicates a breakdown of the normal mechanisms of the red cell proliferation and delivery. In man, normal production of blood cells occurs in the extravascular spaces of the bone marrow - (hemopoietic compartment), mature cells being delivered into circulation in an orderly fashion according to body demand. The factors controlling the movement of mature cells from the hemopoietic compartment into the circulation are poorly understood. Nucleated red cells may actively participate in this movement as they are capable of ameboid motion. Minor variations in intramedullary pressure, resulting from cellular proliferation, may also be a factor. It is helpful to consider that the hemopoietic tissue is located within the non-expansile bony cavity of fixed volume. As each new cell grows, one must depart so as to maintain the fixed volume. Thus, cell traffic out of the marrow cavity varies proportionately with the intensity of cell proliferation in the hemopoietic compartment.From a pathophysiologic standpoint, erythroblastemia may occur under four circumstances:The rate of hemopoietic cell production may override the capacity of the "sinus sieve" to keep the blood free of nucleated red cells. The hyperproliferation of erythropoietic tissue within the non-expansile confines of the bone cavity may force more nucleated red cells into circulation than the sinus sieve or the splenic ifiter can screen out. This erythroblastemia is usually limited to a few fairly mature nucleated red cells, the number of which reflects the severity of the underlying disease. In such disorders an appropriate reticulocytosis is usually present.
On the other hand, when the increase in demand for erythrocyte is acute, the sinus sieve is overwhelmed and some nucleated red cells may escape into circulation before the development of significant erythroid hyperplasia. This may be the mechanism of erythroblastemia in severe blood loss with attendant hypotension and hypovolemia. This mechanism is probably mediated by an increase in production of erythropoietin as a result of hypoxia. Increase in erythropoietin output may also be responsible for erythroblastemia accompanying hypoxia of severe cardiac failure, pulmonary embolism or severe cor pulmonale. In these situations, the findings of erythroblastemia is often indicative of unfavorable prognosis. Slight to moderate reticulocytosis (up to 8 percent) may be present. Erythroblastemia is restricted to fairly mature nucleated red cells, but occasional immature granulocytes may also be seen. Morphologic abnormalities of red cells are usually absent.
A third cause of erythroblastemia is mechanical disruption of the normal marrow structure by infiltrative diseases, notably metastatic carcinoma. This form of erythroblastemia is usually accompanied by the presence of circulating immature granulocytes and severe anemia (leukoerythroblastic anemia) and carries a poor prognosis. The circulating nucleated red cells may be in all stages of developmental maturation. It is of interest that not every metastatic carcinoma with marrow involvement is associated with erythroblastemia. Some tumors (prostate, breast, lung) show a greater tendency than others to produce this phenomenon. The reason for this is not clear.
Another cause of erythroblastemia is hemopoiesis within the intravascular space-a phenomenon that bypasses the sinus sieve. This is seen in the myeloproliferative disorders, notably myeloid metaplasia, polycythemia vera, and chronic granulocytic leukemia. In these disorders, particularly myeloid metaplasia, with or without myelofibrosis, poikilocytosis is often profound as deformed cells proliferate directly within the blood stream in teardrop and other abnormal forms. The appearance of bizarre platelets and immature granulocytes in the circulation (leukoerythroblastosis) is also explicable on the basis of intravascular hemopoiesis. As may be expected, nucleated red cells in all stages of development (basophilic, polychromatophilic, orthochromatic) are seen in the blood. Mild reticulocytosis (2 to 5 percent) is usually present as well.
Circulating hemopoietic cells, irrespective of the way in which they enter circulation, are trapped in the spleen, and if such cells are able to undergo mitosis, they may form small hemopoietic foci. Some investigators have implicated such foci of hemopoiesis as the pathogenetic cause of erythroblastemia. These foci are, however, extravascular, being located in the cordal compartment of splenic red pulp. They are the result of erythroblastemia. Extramedullary hemopoiesis may be intravascular or extravascular. To implicate extramedullary hemopoiesis as a cause of erythroblastemia, intravascular hemopoiesis must be demonstrable.Symptoms:Cyanosis and hypoxemiaare invariably present.
Persistent fatigue, pale or yellowish skin, and frequent headaches.
Diarrhea, nausea, and a loss of appetite.
Physical weakness with minimal exertion, an enlargement of the liver, shortness of breath, and the expulsion of bile through urine and fecal matter.
Diagnosis:Blood studies usually show a low color index, marked anisocytosis, and poikilocytosis, immaturity of red cells, increase in platelets and a polymorphonuclear leukocytosis with numerous immature cells. Reticulocytes are somewhat increased constituting 5-20% of the red cells. Fragility tests have shows an prolongation of the span of hemolysis, beginning at 0.50 to 0.20. The red cells may have certain specific characteristics. They tend to be large and to have an uneven distribution of hemoglobin. An abnormality of the stroma has also been described, which, however, may also be encountered in sickle-cell anemia. Increased blood destruction occurs but is not so marked as in sickle-cell anemia. The bilirubin content of the blood is increased, the Van den Bergh reaction is indirect.The significance of erythroblastemia must be considered in the context of the clinical setting in which it is found. Interpretation should take into account the number and spectrum of maturity of the nucleated red cells; the presence or absence of reticulocytosis and other red cell abnormalities (for example, poikilocytosis); the presence or absence of anemia; the presence or absence of circulating immature granulocytes or bizarre platelets and the presence or absence of the spleen. Circulating nucleated red cells indicate intravascular hemopoiesis or disruption of marrow structure or the inability of the bone marrow's screen mechanism to prevent their passage into circulation. In the latter situations, it usually indicates an unfavorable prognosis.Treatment:The incremental advance in the available automated extended red blood cell measurements, the reticulocytes count, the immature reticulocyte fraction (IRF) and the NRBC (nucleated red blood cell) count, add a dynamic dimension to the diagnostic value. By means of multivariate measurement combinations these “state of the art” multi-parameter analyzers can now support the diagnostic and patient monitoring requirements of Modern medicine, particularly for the new treatment modalities of high dose chemotherapy, growth factor therapy and transplantation for malignant disease. Examples are the bivariate plot of reticulocyte count and immature reticulocytes in diagnosis and that of hemoglobin concentration and NRBC count for monitoring the transfusion requirements of patients with thalassemia major to name but two. It must be the goal of automated-hematology devices to maximize the useful clinical information obtained from a single sample of EDTA (ethylenediaminetetraacetic acid) blood not only in the interests of good patient care but to reduce the demands on, and costs incurred by the Laboratory.NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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