Normal bone marrow, microscopic

At medium-power magnification, normal marrow is seen to be a mixture of hematopoietic elements and adipose tissue. This marrow is taken from the posterior iliac crest of a middle-aged person, so it is about 50% cellular at age 50, declining by 10% per decade thereafter. In very elderly individuals, most remaining hematopoiesis is concentrated in vertebrae, sternum, and ribs. The erythroid islands (♦) and granulocytic precursors (▲) form the bulk of the hematopoietic components, admixed with steatocytes (∗). The large multinucleated cells are megakaryocytes (+). Small numbers of lymphocytes, mainly memory B cells, and plasma cells secreting immunoglobulins are present.

Normal bone marrow, microscopic

At higher magnification, megakaryocytes (∗), erythroid islands (♦), and granulocytic precursors (▲) are present. The normal myeloid-to-erythroid ratio is about 2:1 to 3:1. A high proliferation rate from CD34+ stem cells differentiating into various colony-forming units under the influence of c- KIT ligand is needed because granulocytes last less than 1 day in circulation, platelets less than 1 week, and red blood cells (RBCs) about 120 days. Erythropoietin stimulates RBC production, thrombopoietin platelet formation, granulocyte-macrophage colony-stimulating factor, granulocyte and monocyte-macrophage proliferation, and granulocyte colony-stimulating factor neutrophil production.

Normal bone marrow smear, microscopic

In this normal bone marrow smear at high magnification, megakaryocytes (∗), erythroid precursors (♦), and granulocytic precursors (▲) are present. Erythroid precursors are nucleated, but the nucleus is normally lost before mature red blood cells (RBCs) are released into the circulation. Newly released RBCs, called reticulocytes, have a slightly increased mean corpuscular volume and increased RNA content that imparts a slightly basophilic appearance, and this RNA can be precipitated by supravital staining for identification and enumeration (the “retic” count). Platelets are formed by budding off megakaryocyte cytoplasm.

Normal peripheral blood smear, microscopic

These are happy, normal red blood cells (RBCs) with a zone of central pallor about one third the size of the RBC diameter. These RBCs show minimal variation in size (anisocytosis) and shape (poikilocytosis). A small blue-staining platelet (▲) is present. A normal mature lymphocyte on the left can be compared with a segmented neutrophil (polymorphonuclear leukocyte) on the right. An RBC is about two thirds the size of a normal lymphocyte. The hemoglobin in RBCs supplies most of the oxygen-carrying capacity of blood, with a small fraction as dissolved oxygen.

Rouleaux formation, microscopic

The red blood cells (RBCs) here have stacked together in long chains, known as “rouleaux formation.” This phenomenon occurs with an increase in serum proteins, particularly acute phase reactants such as fibrinogen, C-reactive protein, and globulins. Such long chains of RBCs sediment more readily when left to stand in a column. This is the mechanism for measuring the erythrocyte sedimentation rate (“sed rate”), which increases nonspecifically when inflammation is present and cytokines such as Interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and interferon-γ are released. The “sed rate” is a nonspecific indicator of an inflammatory process.

Hemolytic anemia, microscopic

This peripheral blood smear shows many smaller red blood cells (RBCs) lacking central pallor—spherocytes (→). The larger, bluish-staining reticulocytes (◀) come from increased marrow release to compensate for RBC loss, such as an autoimmune hemolytic anemia from antibody coating the RBC surface membranes. Subsequently, portions of RBC membranes are removed, mostly in the spleen, decreasing RBC size (microcytosis). Reduction in size or number of RBCs results in anemia. The bone marrow can respond to anemia with increased erythropoiesis, indicated by an elevated reticulocyte count. An increased RBC turnover with rapid recycling leads to unconjugated (indirect) hyperbilirubinemia.

Hereditary spherocytosis, microscopic

Many of these red blood cells (RBCs) are small (compare with the lymphocyte) and lack the central zone of pallor and have lost the biconcave shape. These RBCs are known as spherocytes. In hereditary spherocytosis, an autosomal dominant condition most frequent in northern Europeans, there is a lack of key RBC cytoskeletal membrane proteins such as spectrin or ankyrin, leading to RBC membrane instability that forces the cell to form the smallest volume possible—a sphere. In the laboratory, this leads to increased osmotic fragility. Spherocytes do not survive in circulation for as long as normal RBCs and are removed in the spleen. Note the reticulocyte (◀) from increased bone marrow production of RBCs.

Glucose-6-phosphate dehydrogenase deficiency, microscopic

This peripheral blood smear with methylene blue stain shows pale peripheral red blood cell (RBC) Heinz body inclusions (←) in glucose-6-phosphate dehydrogenase deficiency. The defect is in the hexose monophosphate (HMP) shunt, which helps protect RBCs from oxidation. This X-linked disorder, found in 12% of male African Americans, is also seen in individuals from the Mediterranean region, including Italy, Greece, and Turkey. It is asymptomatic until stress occurs from infection or ingestion of an oxidizing drug. Older RBCs exposed to oxidizing agents such as primaquine, sulfa drugs, the nitrofurantoin family, aspirin, and phenacetin undergo hemolysis. Foods like fava beans may have a similar effect. Laboratory findings include anemia, reticulocytosis, indirect hyperbilirubinemia, and decreased haptoglobin.

Hemoglobin electrophoresis, cellulose acetate

The hemoglobin in red blood cells can be analyzed by multiple methods to determine the types of hemoglobin present to diagnose hemoglobinopathies. Shown here in lane 1 is an infant with sickle cell anemia (Hgb S) and significant fetal hemoglobin (Hgb F) production; the heterozygous state of sickle cell trait is shown in lane 4. Lane 2 illustrates homozygous Hgb C, and lane 3 heterozygous Hgb C disease.

Sickle cell anemia, microscopic

Many sickled red blood cells (RBCs) (→) in peripheral blood are present in sickle cell crisis. The abnormal hemoglobin S is prone to polymerization with tactoid formation when oxygen tension is low, and the RBCs change shape to long, thin sickle forms that do not exchange oxygen well and are prone to stick together, plugging smaller vessels and leading to decreased blood flow with ischemia from decreased oxygen delivery to tissues, with clinical findings such as acute abdominal pain, chest pain, and back pain. Hemoglobin electrophoresis in sickle cell disease shows 90% to 95% Hgb S, 1% to 3% Hgb A2, and 5% to 10% Hgb F. In sickle cell trait, there is 40% to 45% Hgb S, 55% to 60% Hgb A1, and normal amounts (1% to 3%) of Hgb A2, and the RBCs have no or minimal sickling.

Sickle cell anemia, gross

The β globin gene defect with Hgb S is a single point mutation with glu → val substitution. Although in early childhood the spleen may be enlarged with sickle cell anemia, continual stasis and trapping of abnormal red blood cells in the spleen leads to extensive infarctions, which eventually reduce splenic size tremendously by adolescence. This is called autosplenectomy. Seen here is the remnant of spleen in a teenage patient with sickle cell anemia. Lack of a spleen predisposes to infections, particularly with encapsulated bacterial organisms such as pneumococcus. In African Americans, the gene frequency for Hgb S is about 1 in 25, with a carrier rate of 1 in 12, and a 1 in 625 chance for sickle cell disease.

Howell-Jolly bodies, microscopic

The red blood cell (RBC) in the center of this peripheral blood smear field contains two dark-blue Howell-Jolly bodies, or inclusions of nuclear chromatin remnants. There is also a nucleated RBC just beneath this RBC. Abnormal and older RBCs approaching their 120-day life span are typically removed by the spleen, with release of bile pigments and carbon monoxide (explaining a normal 1% carboxyhemoglobin blood gas value). Appearance of increased poikilocytosis, anisocytosis, and RBC inclusions on a peripheral blood smear suggests that the spleen is absent. Presence of nucleated RBCs is typical for hemolysis with increased RBC turnover, so that the bone marrow is stressed to release not only reticulocytes, but also more immature RBC precursors.

Hemoglobin SC disease, microscopic

Both Hgb S and Hgb C are present within these red blood cells (RBCs). With SC disease, the RBCs may sickle, but not as commonly or severely as with Hgb SS disease (sickle cell anemia), though there can be chronic hemolytic anemia. The Hgb C leads to the formation of “target” cells—RBCs that have a central reddish dot within the zone of pallor (↓) in this peripheral blood smear. The rectangular RBC (←) is indicative of a Hgb C crystal, which is also characteristic of Hgb C disease. The abnormal β globin gene has an amino acid substitution at position 6 (β6Glu-Lys); this mutation arose in West Africa.