Chapter 058. Anemia and Polycythemia (Part 6)

Uremia. The red cells in uremia may acquire numerous, regularly spaced, small spiny projections. Such cells, called burr cells or echinocytes, are readily distinguishable from irregularly spiculated acanthocytes shown in Fig. 58-11.Figure 58-11Spur cells. Spur cells are recognized as distorted red cells containing several irregularly distributed thornlike projections. Cells with this morphologic abnormality are also called acanthocytes. (From Hillman et al.)Reticulocyte CountAn accurate reticulocyte count is key to the initial classification of anemia. Normally, reticulocytes are red cells that have been recently released from thebone marrow. ...
Nội dung trích xuất từ tài liệu:
Chapter 058. Anemia and Polycythemia (Part 6) Chapter 058. Anemia and Polycythemia (Part 6)Figure 58-10 Uremia. The red cells in uremia may acquire numerous, regularly spaced,small spiny projections. Such cells, called burr cells or echinocytes, are readilydistinguishable from irregularly spiculated acanthocytes shown in Fig. 58-11. Figure 58-11 Spur cells. Spur cells are recognized as distorted red cells containingseveral irregularly distributed thornlike projections. Cells with this morphologicabnormality are also called acanthocytes. (From Hillman et al.) Reticulocyte Count An accurate reticulocyte count is key to the initial classification of anemia.Normally, reticulocytes are red cells that have been recently released from thebone marrow. They are identified by staining with a supravital dye thatprecipitates the ribosomal RNA (Fig. 58-12). These precipitates appear as blue orblack punctate spots. This residual RNA is metabolized over the first 24–36 h ofthe reticulocytes lifespan in circulation. Normally, the reticulocyte count rangesfrom 1–2% and reflects the daily replacement of 0.8–1.0% of the circulating redcell population. A reticulocyte count provides a reliable measure of red cellproduction. Figure 58-12 Reticulocytes. Methylene blue stain demonstrates residual RNA in newlymade red cells. (From Hillman et al.) In the initial classification of anemia, the patients reticulocyte count iscompared with the expected reticulocyte response. In general, if the EPO anderythroid marrow responses to moderate anemia [hemoglobin < 100 g/L (10g/dL)] are intact, the red cell production rate increases to two to three timesnormal within 10 days following the onset of anemia. In the face of establishedanemia, a reticulocyte response less than two to three times normal indicates aninadequate marrow response. In order to use the reticulocyte count to estimate marrow response, twocorrections are necessary. The first correction adjusts the reticulocyte count basedon the reduced number of circulating red cells. With anemia, the percentage ofreticulocytes may be increased while the absolute number is unchanged. Tocorrect for this effect, the reticulocyte percentage is multiplied by the ratio of thepatients hemoglobin or hematocrit to the expected hemoglobin/hematocrit for theage and gender of the patient (Table 58-4). This provides an estimate of thereticulocyte count corrected for anemia. In order to convert the correctedreticulocyte count to an index of marrow production, a further correction isrequired, depending on whether some of the reticulocytes in circulation have beenreleased from the marrow prematurely. For this second correction, the peripheralblood smear is examined to see if there are polychromatophilic macrocytespresent. These cells, representing prematurely released reticulocytes, are referredto as shift cells, and the relationship between the degree of shift and thenecessary shift correction factor is shown in Fig. 58-13. The correction isnecessary because these prematurely released cells survive as reticulocytes incirculation for >1 day, thereby providing a falsely high estimate of daily red cellproduction. If polychromasia is increased, the reticulocyte count, already correctedfor anemia, should be divided again by a factor of 2 to account for the prolongedreticulocyte maturation time. The second correction factor varies from 1–3depending on the severity of anemia. In general, a correction of 2 is commonlyused. An appropriate correction is shown in Table 58-4. If polychromatophiliccells are not seen on the blood smear, the second correction is not required. Thenow doubly corrected reticulocyte count is the reticulocyte production index, andit provides an estimate of marrow production relative to normal.