Some of the relevant findings in peripheral blood, enlarged lymph nodes, and bone marrow are illustrated in this chapter. Systematic histologic examination of the bone marrow and lymph nodes is beyond the scope of a general medicine textbook. However, every internist should know how to examine a peripheral blood smear.
The examination of a peripheral blood smear is one of the most informative exercises a physician can perform. Although advances in automated technology have made the examination of a peripheral blood smear by a physician seem less important, the technology is not a completely satisfactory replacement for a blood smear interpretation by a trained medical professional who also knows the patient's clinical history, family history, social history, and physical findings. It is useful to ask the laboratory to generate a Wright's-stained peripheral blood smear and examine it.
The best place to examine blood cell morphology is the feathered edge of the blood smear where red cells lie in a single layer, side by side, just barely touching one another but not overlapping. The author's approach is to look at the smallest cellular elements, the platelets, first and work his way up in size to red cells and then white cells.
Using an oil immersion lens that magnifies the cells 100-fold, one counts the platelets in five to six fields, averages the number per field, and multiplies by 20,000 to get a rough estimate of the platelet count. The platelets are usually 1–2 μm in diameter and have a blue granulated appearance. There is usually 1 platelet for every 20 or so red cells. Of course, the automated counter is much more accurate, but gross disparities between the automated and manual counts should be assessed. Large platelets may be a sign of rapid platelet turnover, as young platelets are often larger than old ones; alternatively, certain rare inherited syndromes can produce large platelets. Platelet clumping visible on the smear can be associated with falsely low automated platelet counts. Similarly, neutrophil fragmentation can be a source of falsely elevated automated platelet counts.
Next one examines the red blood cells. One can gauge their size by comparing the red cell with the nucleus of a small lymphocyte. Both are normally about 8 μm wide. Red cells that are smaller than the small lymphocyte nucleus may be microcytic; those larger than the small lymphocyte nucleus may be macrocytic. Macrocytic cells also tend to be more oval than spherical in shape and are sometimes called macroovalocytes. The automated mean corpuscular volume (MCV) can assist in making a classification. However, some patients may have both iron and vitamin B12 deficiency, which will produce an MCV in the normal range but wide variation in red cell size. When the red cells vary greatly in size, anisocytosis is said to be present. When the red cells vary greatly in shape, poikilocytosis is said to be present. The electronic cell counter provides an independent assessment of variability in red cell size. It measures the range of red cell volumes and reports the results as "red cell distribution width" (RDW). This value is calculated from the MCV; thus, cell width is not being measured but cell volume is. The term is derived from the curve displaying the frequency of cells at each volume, also called the distribution. The width of red cell volume distribution curve is what determines the RDW. The RDW is calculated as follows: RDW = (standard deviation of MCV ÷ mean MCV) × 100. In the presence of morphologic anisocytosis, RDW (normally 11–14%) increases to 15–18%. The RDW is useful in at least two clinical settings. In patients with microcytic anemia, the differential diagnosis is generally between iron deficiency and thalassemia. In thalassemia, the small red cells are generally of uniform size with a normal small RDW. In iron deficiency, the size variability and the RDW are large. In addition, a large RDW can suggest a dimorphic anemia when a chronic atrophic gastritis can produce both vitamin B12 malabsorption to produce macrocytic anemia and blood loss to produce iron deficiency. In such settings, RDW is also large. An elevated RDW also has been reported as a risk factor for all-cause mortality in population-based studies (Patel KV, Ferrucci L, Ershler WB, et al: Red blood cell distribution width and the risk of death in middle-aged and older adults. Arch Intern Med 169:515, 2009), a finding that is unexplained currently.
After red cell size is assessed, one examines the hemoglobin content of the cells. They are either normal in color (normochromic) or pale in color (hypochromic). They are never "hyperchromic." If more than the normal amount of hemoglobin is made, the cells get larger—they do not become darker. In addition to hemoglobin content, the red cells are examined for inclusions. Red cell inclusions are the following:
Basophilic stippling—diffuse fine or coarse blue dots in the red cell usually representing RNA residue—especially common in lead poisoning
Howell-Jolly bodies—dense blue circular inclusions that represent nuclear remnants—their presence implies defective splenic function
Nuclei—red cells may be released or pushed out of the marrow prematurely before nuclear extrusion—often implies a myelophthisic process or a vigorous narrow response to anemia, usually hemolytic anemia
Parasites—red cell parasites include malaria and babesia
Polychromatophilia—the red cell cytoplasm has a bluish hue, reflecting the persistence of ribosomes still actively making hemoglobin in a young red cell
Vital stains are necessary to see precipitated hemoglobin called Heinz bodies.
Red cells can take on a variety of different shapes. All abnormally shaped red cells are poikilocytes. Small red cells without the central pallor are spherocytes; they can be seen in hereditary spherocytosis, hemolytic anemias of other causes, and clostridial sepsis. Dacrocytes are teardrop-shaped cells that can be seen in hemolytic anemias, severe iron deficiency, thalassemias, myelofibrosis, and myelodysplastic syndromes. Schistocytes are helmet-shaped cells that reflect microangiopathic hemolytic anemia or fragmentation on an artificial heart valve. Echinocytes are spiculated red cells with the spikes evenly spaced; they can represent an artifact of abnormal drying of the blood smear or reflect changes in stored blood. They also can be seen in renal failure and malnutrition and are often reversible. Acanthocytes are spiculated red cells with the spikes irregularly distributed. This process tends to be irreversible and reflects underlying renal disease, abetalipoproteinemia, or splenectomy. Elliptocytes are elliptical-shaped red cells that can reflect an inherited defect in the red cell membrane, but they also are seen in iron deficiency, myelodysplastic syndromes, megaloblastic anemia, and thalassemias. Stomatocytes are red cells in which the area of central pallor takes on the morphology of a slit instead of the usual round shape. Stomatocytes can indicate an inherited red cell membrane defect and also can be seen in alcoholism. Target cells have an area of central pallor that contains a dense center, or bull's eye. These cells are seen classically in thalassemia, but they are also present in iron deficiency, cholestatic liver disease, and some hemoglobinopathies. They also can be generated artifactually by improper slide making.
One last feature of the red cells to assess before moving to the white blood cells is the distribution of the red cells on the smear. In most individuals, the cells lie side by side in a single layer. Some patients have red cell clumping (called agglutination) in which the red cells pile upon one another; it is seen in certain paraproteinemias and autoimmune hemolytic anemias. Another abnormal distribution involves red cells lying in single cell rows on top of one another like stacks of coins. This is called rouleaux formation and reflects abnormal serum protein levels.
Finally, one examines the white blood cells. Three types of granulocytes are usually present: neutrophils, eosinophils, and basophils, in decreasing frequency. Neutrophils are generally the most abundant white cell. They are round, are 10–14 μm wide, and contain a lobulated nucleus with two to five lobes connected by a thin chromatin thread. Bands are immature neutrophils that have not completed nuclear condensation and have a U-shaped nucleus. Bands reflect a left shift in neutrophil maturation in an effort to make more cells more rapidly. Neutrophils can provide clues to a variety of conditions. Vacuolated neutrophils may be a sign of bacterial sepsis. The presence of 1- to 2-μm blue cytoplasmic inclusions, called Döhle bodies, can reflect infections, burns, or other inflammatory states. If the neutrophil granules are larger than normal and stain a darker blue, "toxic granulations" are said to be present, and they also suggest a systemic inflammation. The presence of neutrophils with more than five nuclear lobes suggests megaloblastic anemia. Large misshapen granules may reflect the inherited Chédiak-Higashi syndrome.
Eosinophils are slightly larger than neutrophils, have bilobed nuclei, and contain large red granules. Diseases of eosinophils are associated with too many of them rather than any morphologic or qualitative change. They normally total less than one-thirtieth the number of neutrophils. Basophils are even more rare than eosinophils in the blood. They have large dark blue granules and may be increased as part of chronic myeloid leukemia.
Lymphocytes can be present in several morphologic forms. Most common in healthy individuals are small lymphocytes with a small dark nucleus and scarce cytoplasm. In the presence of viral infections, more of the lymphocytes are larger, about the size of neutrophils, with abundant cytoplasms and a less condensed nuclear chromatin. These cells are called reactive lymphocytes. About 1% of lymphocytes are larger and contain blue granules in a light blue cytoplasm; they are called large granular lymphocytes. In chronic lymphoid leukemia, the small lymphocytes are increased in number, and many of them are ruptured in making the blood smear, leaving a smudge of nuclear material without a surrounding cytoplasm or cell membrane; they are called smudge cells and are rare in the absence of chronic lymphoid leukemia.
Monocytes are the largest white blood cells, ranging from 15 to 22 μm in diameter. The nucleus can take on a variety of shapes but usually appears to be folded; the cytoplasm is gray.
Abnormal cells may appear in the blood. Most often the abnormal cells originate from neoplasms of bone marrow–derived cells, including lymphoid cells, myeloid cells, and occasionally red cells. More rarely, other types of tumors can get access to the bloodstream, and rare epithelial malignant cells may be identified. The chances of seeing such abnormal cells is increased by examining blood smears made from buffy coats, the layer of cells that is visible on top of sedimenting red cells when blood is left in the test tube for an hour. Smears made from finger sticks may include rare endothelial cells.
Normal peripheral blood smear. Small lymphocyte in center of field. Note that the diameter of the red blood cell is similar to the diameter of the small lymphocyte nucleus.
Reticulocyte count preparation. This new methylene blue–stained blood smear shows large numbers of heavily stained reticulocytes (the cells containing the dark blue–staining RNA precipitates).
Hypochromic microcytic anemia of iron deficiency. Small lymphocyte in field helps assess the red blood cell size.
Iron deficiency anemia next to normal red blood cells. Microcytes (right panel) are smaller than normal red blood cells (cell diameter <7 μm) (left panel) and may or may not be poorly hemoglobinized (hypochromic).
Polychromatophilia. Note large red cells with light purple coloring.
Macrocytosis. These cells are both larger than normal (mean corpuscular volume >100) and somewhat oval in shape. Some morphologists call these cells macroovalocytes.
Hypersegmented neutrophils. Hypersegmented neutrophils (multilobed polymorphonuclear leukocytes) are larger than normal neutrophils with five or more segmented nuclear lobes. They are commonly seen with folic acid or vitamin B12 deficiency.
Spherocytosis. Note small hyperchromatic cells without the usual clear area in the center.
Rouleaux formation. Small lymphocyte in center of field. These red cells align themselves in stacks and are related to increased serum protein levels.
Red cell agglutination. Small lymphocyte and segmented neutrophil in the upper left center. Note the irregular collections of aggregated red cells.
Fragmented red cells. Heart valve hemolysis.
Sickle cells. Homozygous sickle cell disease. A nucleated red cell and neutrophil are also in the field.
Target cells. Target cells are recognized by the bull's-eye appearance of the cell. Small numbers of target cells are seen with liver disease and thalassemia. Larger numbers are typical of hemoglobin C disease.
Elliptocytosis. Small lymphocyte in center of field. Elliptical shape of red cells related to weakened membrane structure, usually due to mutations in spectrin.
Stomatocytosis. Red cells characterized by a wide transverse slit or stoma. This often is seen as an artifact in a dehydrated blood smear. These cells can be seen in hemolytic anemias and in conditions in which the red cells are overhydrated or dehydrated.
Acanthocytosis. Spiculated red cells are of two types: acanthocytes are contracted dense cells with irregular membrane projections that vary in length and width; echinocytes have small, uniform, and evenly spaced membrane projections. Acanthocytes are present in severe liver disease, in patients with abetalipoproteinemia, and in rare patients with McLeod blood group. Echinocytes are found in patients with severe uremia, in glycolytic red cell enzyme defects, and in microangiopathic hemolytic anemia.
Howell-Jolly bodies. Howell-Jolly bodies are tiny nuclear remnants that normally are removed by the spleen. They appear in the blood after splenectomy (defect in removal) and with maturation/dysplastic disorders (excess production).
Teardrop cells and nucleated red blood cells characteristic of myelofibrosis. A teardrop-shaped red blood cell (left panel) and a nucleated red blood cell (right panel) as typically seen with myelofibrosis and extramedullary hematopoiesis.
Myelofibrosis of the bone marrow. Total replacement of marrow precursors and fat cells by a dense infiltrate of reticulin fibers and collagen (H&E stain).
Reticulin stain of marrow myelofibrosis. Silver stain of a myelofibrotic marrow showing an increase in reticulin fibers (black-staining threads).
Stippled red cell in lead poisoning. Mild hypochromia. Coarsely stippled red cell.
Heinz bodies. Blood mixed with hypotonic solution of crystal violet. The stained material is precipitates of denatured hemoglobin within cells.
Giant platelets. Giant platelets, together with a marked increase in the platelet count, are seen in myeloproliferative disorders, especially primary thrombocythemia.
Normal granulocytes. The normal granulocyte has a segmented nucleus with heavy, clumped chromatin; fine neutrophilic granules are dispersed throughout the cytoplasm.
Normal monocytes. The film was prepared from the buffy coat of the blood from a normal donor. L, lymphocyte; M monocyte; N, neutrophil.
Normal eosinophils. The film was prepared from the buffy coat of the blood from a normal donor. E, eosinophil; L, lymphocyte. N, neutrophil;
Normal basophil. The film was prepared from the buffy coat of the blood from a normal donor. B, basophil; L, lymphocyte.
Pelger-Hüet anomaly. In this benign disorder, the majority of granulocytes are bilobed. The nucleus frequently has a spectacle-like, or "pince-nez," configuration.
Döhle body. Neutrophil band with Döhle body. The neutrophil with a sausage-shaped nucleus in the center of the field is a band form. Döhle bodies are discrete, blue-staining nongranular areas found in the periphery of the cytoplasm of the neutrophil in infections and other toxic states. They represent aggregates of rough endoplasmic reticulum.
Chédiak-Higashi disease. Note giant granules in neutrophil.
Normal bone marrow. Low-power view of normal adult marrow (H&E stain), showing a mix of fat cells (clear areas) and hematopoietic cells. The percentage of the space that consists of hematopoietic cells is referred to as marrow cellularity. In adults, normal marrow cellularity is 35–40%. If demands for increased marrow production occur, cellularity may increase to meet the demand. As people age, the marrow cellularity decreases and the marrow fat increases. Patients >70 years old may have a 20–30% marrow cellularity.
Aplastic anemia bone marrow. Normal hematopoietic precursor cells are virtually absent, leaving behind fat cells, reticuloendothelial cells, and the underlying sinusoidal structure.
Metastatic cancer in the bone marrow. Marrow biopsy specimen infiltrated with metastatic breast cancer and reactive fibrosis (H&E stain).
Lymphoma in the bone marrow. Nodular (follicular) lymphoma infiltrate in a marrow biopsy specimen. Note the characteristic paratrabecular location of the lymphoma cells.
Erythroid hyperplasia of the marrow. Marrow aspirate specimen with a myeloid/erythroid ratio (M/E ratio) of 1:1–2, typical for a patient with a hemolytic anemia or one recovering from blood loss.
Myeloid hyperplasia of the marrow. Marrow aspirate specimen showing a myeloid/erythroid ratio of ≥ 3:1, suggesting either a loss of red blood cell precursors or an expansion of myeloid elements.
Megaloblastic erythropoiesis. High-power view of megaloblastic red blood cell precursors from a patient with a macrocytic anemia. Maturation is delayed, with late normoblasts showing a more immature-appearing nucleus with a lattice-like pattern with normal cytoplasmic maturation.
Prussian blue staining of marrow iron stores. Iron stores can be graded on a scale of 0 to 4+. A: a marrow with excess iron stores (>4+); B: normal stores (2–3+); C: minimal stores (1+); and D: absent iron stores (0).
Ringed sideroblast. An orthochromatic normoblast with a collar of blue granules (mitochondria encrusted with iron) surrounding the nucleus.
Acute myeloid leukemia. Leukemic myeloblast with an Auer rod. Note two to four large, prominent nucleoli in each cell.
Acute promyelocytic leukemia. Note prominent cytoplasmic granules in the leukemia cells.
Acute erythroleukemia. Note giant dysmorphic erythroblasts; two are binucleate, and one is multinucleate.
Acute lymphoblastic leukemia.
Burkitt's leukemia, acute lymphoblastic leukemia.
Chronic myeloid leukemia in the peripheral blood.
Chronic lymphoid leukemia in the peripheral blood.
Sézary's syndrome. Lymphocytes with frequently convoluted nuclei (Sézary cells) in a patient with advanced mycosis fungoides.
Adult T cell leukemia. Peripheral blood smear showing leukemia cells with typical "flower-shaped" nucleus.
Follicular lymphoma in a lymph node. The normal nodal architecture is effaced by nodular expansions of tumor cells. Nodules vary in size and contain predominantly small lymphocytes with cleaved nuclei along with variable numbers of larger cells with vesicular chromatin and prominent nucleoli.
Diffuse large B cell lymphoma in a lymph node. The neoplastic cells are heterogeneous but predominantly large cells with vesicular chromatin and prominent nucleoli.
Burkitt's lymphoma in a lymph node. Burkitt's lymphoma with starry-sky appearance. The lighter areas are macrophages attempting to clear dead cells.
Erythrophagocytosis accompanying aggressive lymphoma. The central macrophage is ingesting red cells, neutrophils, and platelets. (Courtesy of Dr. Kiyomi Tsukimori, Kyushu University, Fukuoka, Japan.)
Hodgkin's disease. A Reed-Sternberg cell is present near the center of the field; a large cell with a bilobed nucleus and prominent nucleoli giving an "owl's eyes" appearance. The majority of the cells are normal lymphocytes, neutrophils, and eosinophils that form a pleiomorphic cellular infiltrate.
Lacunar cell; Reed-Sternberg cell variant in nodular sclerosing Hodgkin's disease. High-power view of single mononuclear lacunar cell with retracted cytoplasm in a patient with nodular sclerosing Hodgkin's disease.
Color serum in hemoglobinemia. The distinctive red coloration of plasma (hemoglobinemia) in a spun blood sample in a patient with intravascular hemolysis.