Erythroid Information and Courses from MediaLab, Inc.

Anemia is fatal.Red blood cell (RBC) count is increased.Hemoglobin (Hb) is severely decreased.Mean corpuscular volume (MCV) is decreased. Mean corpuscular hemoglobin concentration (MCHC) is decreased.Red cell distribution width (RDW) is increased.RBC morphology shows slight hypochromic microcytosis with codocytes, schizocytes, nucleated RBCs.Reticulocytes are increased.Hb electrophoresis demonstrates abnormal pattern on cord blood: Hb A - absentHb Bart's - 80-90%Hb Portland - 0-20%Bone marrow demonstrates marked erythroid hyperplasia.

Anemia is mild to absent.RBC count is increased.Hb is slightly decreased.MCV is decreased. MCHC is slightly decreased.RDW is normal to slightly increased.Red Blood Cell morphology shows slight hypochromic microcytosis.Reticulocytes are normal to slightly increased.Hb electrophoresis demonstrates a normal pattern in adults:Hb A - 97-98% Hb A2 - 1-2.5% Hb F - <1%. Neonates have 5-15% Bart's Hemoglobin (gamma chain tetramers).Hb H inclusions are rarely seen.Bone marrow demonstrates erythroid hyperplasia.

In thalassemia, there is often an excess production or accumulation of globin chains whose genes are not affected by the deletion.In beta thalassemia, this may be seen as an increase in gamma chain and delta chain production, leading to increased levels of hemoglobin F and A2 respectively.Excess alpha chains may also form tetramers which often lead to red cell membrane damage and decreased red cell deformability. This leads to a hemolytic anemia. Adding to the anemia is a decrease in the total amount of hemoglobin produced in spite of the erythroid hyperplasia of the bone marrow.

Once absorbed through the mucosal cells of the duodenum, iron is bound to a carrier plasma protein, transferrin (Tf), for movement to sites of utilization. Almost all iron in plasma is bound to Tf, and most Tf-bound iron is carried to the bone marrow to be incorporated into developing erythrocytes. Transferrin is normally about 20% to 40% saturated with iron. (5)Transferrin releases iron to specific transferrin receptors (TfRs) for movement into cells. Transferrin receptors are found on all cells, but are found in relatively high concentration in erythroid precursors, hepatocytes, and placental cells. When the capacity of plasma Tf to bind iron is exceeded, i.e., transferrin saturation (TS) is higher than normal, excess iron is taken up by hepatocytes and other cells. A brief summary of iron metabolism is illustrated.

In some laboratories the anticoagulated sample is used to prepare concentrated smears. Placing the fluid in a Wintrobe tube and centrifuging it separates the sample into four layers:fat and perivascular cellsplasmabuffy layer - myeloid and nucleated erythroid cellserythrocytesThe volume of each layer is measured using the scale on the Wintrobe tube and then the percentage of each layer is calculated. Next the plasma is removed and a smear is made from the buffy coat and top of the red cell layer. Either the manual push method or cytospin technique may be used to make the smears. They may be stained with a variety of cytochemical stains. Concentrated smears are used to examine cell morphology and demonstrate the presence of abnormal cells when the marrow is hypocellular. The smears cannot be used for differential counts or evaluation of cellularity.

Changes in the distribution of cells in the marrow are most apparent in the first month of life. At birth, granulocyte cells predominate. The myeloid to erythroid (M:E) ratio is somewhat higher in newborns and during infancy than it is later on in childhood and in adults.

The site of iron storage in the bone marrow is the macrophage. This is a bone marrow smear showing a macrophage containing near the top of the smear showing clumps of blue-staining material, which is iron. Notice the number of young red cells (erythroid precursors) clustered around the iron in the lower portion of the slide.

This smear is shown under low power (10x objective) magnification. The reddish cells in the background are mature red blood cells. The dark dots are nucleated erythroid and myeloid precursors. The large dark dot in the middle is a megakaryocyte. Normally, about 5 to 10 megakaryocytes are seen per microscopic field at low power magnification. Clusters of megakaryocytes usually indicate megakaryocytic hyperplasia. Less than 2 megakaryocytes per low power field may mean megakaryocytic hypoplasia.

The normal cellularity has been described as 50%. Therefore, about 40% of the cells would be myeloid (granulocytic) and 10% erythroid. Since cellularity and distribution may vary from one area of the marrow to another, an acceptable range for percentages of myeloid and erythroid cells would be:Myeloid cells 25-55%Erythroid cells 8-14%

To help you learn to differentiate myeloid cells and erythrocytes under high power, some slides showing thinner areas than would normally be used for determination of the M:E ratio have been included. Erythroid cells are shown at the arrows.

An increased M:E ratio is present in this field. Many more myeloid cells are present than erythroid cells. The M:E ratio is approximately 25:1.

Another example of a decreased M:E ratio in a representative area of the slide. Numerous erythroid precursors are shown by the arrow.

The actual cell count is performed using the oil (100x) objective. This oil immersion field shows a representative counting field. Four granulocytes, a prorubricyte, and two rubricytes are completely visible here. 100 to 500 nucleated cells are generally counted,depending on the cellularity of the smear, and only cells completely visible in the field should be included in the count.

Many of the distorted erythrocytes displayed on the previous page are also present on this one. We see anisocytosis, poikilocytosis, fragmented forms, target cells, and a few Howell-Jolly bodies. Note also circulating nucleated red blood cells (normoblasts). The presence of these normoblasts may represent a premature release from a hyperplastic marrow or, more likely, are due to a lessening of the normal inhibition of erythroid release from the marrow as a result of splenectomy, permitting their earlier entry into the circulation.