The purpose of Nucleated Red Blood Cells is to describe both normal and abnormal precursors of erythrocytes. The stages of maturation of red blood cells are the best delineated of all of the cell lines. Size is important in assessing cell age as well as the amount of hemoglobin and the amount of basophilia of the cytoplasm due to the presence of RNA. The age is determined also by the concentration and condensation of the nuclear chromatin.
There are three widely used terminologies for red blood cell precursors, each of which is inexact or has created confusion. Starting with the youngest cell of the series, all three nomenclatures use only three terms to identify four mitoses. The classification according to some authors, beginning with Ehrlich, includes terms for a normal or normoblastic and an abnormal or megaloblastic series. The terms, in general, are descriptive of the color of the cytoplasm. For instance, the most mature cell is orthochromatic, meaning the same color as a mature erythrocyte, but all nucleated red blood cells (NRBCs) are slightly polychromatophilic. The terminology of the Sabin and Doan classification is less restrictive, based on their studies that there was only one class of NRBCs and the abnormalities seen in the megaloblastic series were the result of a lack of a maturation factor. To unify the terminology, the Committee for the Clarification of the Nomenclature of Cells and Diseases of the Blood and Blood-forming Organs, composed of well-known hematologists and pathologists, was formed in 1947 (see Suggested Readings). This committee appealed to all hematologists and pathologists for suggestions. They reported their recommendations for the nomenclature for leukocytes and thrombocytes in 1948. The proposed terminology was well-received and it still is the one in use today. However, the nomenclature for the erythrocytic series suggested by the committee (1949) has not been generally accepted because of the use of the Latin prefix "rubri" combined with the Greek suffix "cyte." This has not been acceptable to many purists.
In this and all other units I am going to use the nomenclature suggested by Bessis in his book Blood Smears Reinterpreted, published in 1980 (see Suggested Readings). It is the simplest and easiest for students to learn. It saves the student from groping for the proper term such as pronormoblast or basophilic megaloblastand from the necessity of transposing the term it corresponds to in another system. Bessis used the generic term erythroblast (E) and designated the five stages of amplification from youngest to oldest as E1 to E5 with a final production of 16 erythrocytes from one E1 cell. Even though Bessis' terminology is logical and easily adaptable, it is new and the student must know the old terms to understand the literature. The different classifications of NRBCs will be covered more fully in the following material.
I shall include in this program a description of the abnormal cells found in the bone marrow of patients with megaloblastic anemia due to B12 and folic acid deficiency. I shall also describe other abnormal NRBCs seen in the marrow of patients with refractory anemia, ineffective erythropoiesis, erythroleukemia, preleukemia, and dyserythropoiesis. The next four slides and an additional six slides later in the program are questions for your consideration.
Course Section: 05. Nucleated Red Blood Cells
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