Morphologic Evaluation of Erythrocytes PDF

88 MORPHOLOGIC EVALUATION OF ERYTHROCYTES FIGURE 8-1. Normal adult peripheral blood film showing normo- FIGURE 8-3. Autoagglutination. XIOOO. cytic, normochromic cells. XI000. sible. Cell size and shape cannot always be evaluated in on a blood film when the temperature is below 31°C an...

88 MORPHOLOGIC EVALUATION OF ERYTHROCYTES FIGURE 8-1. Normal adult peripheral blood film showing normo- FIGURE 8-3. Autoagglutination. XIOOO. cytic, normochromic cells. XI000. sible. Cell size and shape cannot always be evaluated in on a blood film when the temperature is below 31°C and the presence of rouleaux formation. particularly below 25°C, which enhances autoantibody When fibrinogen is significantly increased {e.g., in activityBlood film preparation and red cell description infections, tissue necrosis, or pregnancy), rouleaux forms are almost impossible without warming of the blood and long stacks. Even normal red cells may form rouleaux in the glass slide prior to preparation. The clumps of aggluti¬ a thick moist preparation of blood under a coverslip. nated cells disintegrate on warming of the tube. Evalua¬ Spherocytes (see section on Spherocytes later in this chap¬ tion of red cells on films made from warmed samples does ter), on the other hand, cannot form rouleaux. not correlate with red cell indices measured on electronic counters, because cell clumping interferes with accurate AGGLUTINATION automated red cell evaluation. The mean corpuscular vol¬ Erythrocyte agglutination occurs as cells aggregate into ume (Chaps. 9 and 42) is artifactually elevated by clumps random clusters or masses (Eig. 8-3) when exposed to of red cells being counted as single large cells. various red cell antibodies. Thus, the outline of each indi¬ vidual cell is not seen. Rouleaux does not form in the presence of red cell antibodies. Autoagglutination occurs when an individual's red NORMAL MORPHOLOGY cells agglutinate in his or her own plasma or serum that A normal red cell in vivo is a biconcave disc and thus has contains no known specific agglutinins. Sometimes, au¬ been named a discocyte. This shape is well suited for the toagglutination is seen in the blood of apparently normal erythrocyte's task of gas transport and its survival in the individuals but is more likely to be observed in connection circulation.®^ On the slide the cell has been flattened and with certain hemolytic anemias, atypical pneumonia, thus has a round appearance with an area of central pallor staphylococcal infections, and trypanosomiasis.^-^®'^® Au¬ representing the indented region of the disc. Normal red toagglutination may cause anticoagulated blood to ap¬ cells are almost uniform in size, shape, and Hb concentra¬ pear somewhat "grainy" or granular as the tube is being rotated at room temperature.^^ tion. They stain a light red to pink with Wright stain and have a relatively clear central area that gradually leads A common form of autoagglutination is seen in cold to a more deeply stained periphery. The diameter of the agglutinin disease. Here clumps of red cells may be noted central clear area should not be more than one-third of the cell diameter. The gradual transition to deeper stain is an important morphologic feature because it distin¬ guishes normal cells from those with artifactual morpho¬ logic changes (see Artifacts section). There are no inclu¬ sions in normal red cells (Eig. 8-1). The diameter of a normal red cell varies slightly, with a mean of 7 to 8 p,m,®'®^ and is approximately the same size as or slightly smaller than the nucleus of a small lymphocyte (see Color Plate 6-9). Other characteristics include an average thickness of 2.5 (xm/ an average vol¬ ume of 90 fL^^ (1 fL = 10“^®/L), and an average surface area of 160 /xm." The relationship between the limited metabolic fac¬ tors in the non-nucleated erythrocyte and certain proteins within the cell membrane, as well as the external environ¬ FIGURE 8-2. Rouleaux formation by erythrocytes. xIOOO. (From ment, help to maintain the disc shape throughout the life Bell A, Lofsness KG: A photo essay on red cell morphology. J of the cell. If any of these factors is altered, the cell usually Med Technol 3:85, 1986, with permission.) becomes spherical.  Size 89 SIZE disease. However, a cause for macrocytosis often is not ap¬ parent. Average Size Correlated with Mean Patients with liver disease may have macrocytosis; Corpuscular Volume however, whether the macrocytosis is real is debated.^^ NORMOCYTIC Excess plasma cholesterol may be taken up by the red cell membrane, increasing the surface area of the cell. Automated complete blood counts usually include mea¬ When the erythrocyte is spread on the slide, a thin macro¬ surement of the mean corpuscular volume (MCV), which cyte is formed. True macrocytes with MCV exceeding 100 is important because this value indicates the average size fL probably are rare in liver disease without folate defi¬ of erythrocytes. Observation of red cell morphology on ciency.^^ the blood film provides a quality control check on the The presence of oval macrocytes (usually also lacking electronic MCV, as well as the other two red cell indices, central pallor), increased MCV, and low levels of vitamin mean corpuscular hemoglobin (MCH) and mean cor¬ Bi2 or folate suggest a nuclear maturation defect, which puscular hemoblobin concentration (MCHC; Chap. 9). An may be observed in megaloblastic red cells in the bone MCV in the reference range (80 to 100 fL for adults) marrow (Chap. 12). The developmental abnormality of suggests that the red cells are generally of normal size oval macrocytic cells (Fig. 8-4B) is discussed later in (normocytic); however, the film may demonstrate a minor this chapter. population of smaller or larger cells, which may not sig¬ Normal non-nucleated erythrocytes that have just left nificantly alter the MCV. There may be a mixture of differ¬ the bone marrow sinusoids are slightly macrocytic and ent populations of erythrocytes on the film, in which case appear in stained peripheral blood films as diffusely baso¬ the MCV should be in the normal range because of the philic (polychromatophilic) cells. Prematurely released averaging of large and small cell sizes. red cells, called "shift" cells, occur as a result of stimulated erythropoiesis in acute hemolytic anemia. These poly¬ MACROCYTIC chromatophilic cells have an increased MCV, suggesting Erythrocytes are generally described as macrocytic if the a macrocytosis.’^ diameter exceeds 8.5 to 9.0 jxm and the MCV exceeds When the blood glucose is above 600 mg/dL, the 100 fL.^ Automated blood counts have led to increasing high intracellular osmolarity causes fluid to be taken into awareness of macrocytosis with or without anemia.^^ A the cell when it is placed in isotonic diluent. The result slight macrocytosis is observed frequently in hospital pa¬ is a spurious macrocytosis if the count is performed before tients and probably does not warrant investigation. Low equilibration.^’ vitamin or folate levels are common causes of macro¬ With Mycoplasma pneumoniae infection or high titers cytosis (Chap. 12). of cold agglutinins, the MCV may be artifactually high Common causes of a slight to moderate increase in because red cells in doublets or triplets (autoagglutina¬ MCV and of round macrocytes are alcoholism (see Fig. tion) may pass the aperture of an electronic counter."*^ 8-4A) with or without hepatic disease; cancer chemother¬ apy because it interferes with DNA synthesis; chronic hemolytic anemia with reticulocytosis; myeloma; leuke¬ MICROCYTIC mia; lymphoma; metastatic carcinoma; hypothyroidism; Small erythrocytes with reduced volume are termed mi¬ and hemolytic disease of the newborn.^-^^ Large red cells crocytes. Microcytes have normal or decreased Hb content are seen occasionally in stem cell disorders, particularly and reduced, normal, or increased diameters. These elec¬ aplastic anemia, refractory anemia, pure red cell aplasia, tronic and visual changes in morphology are not apparent myelofibrosis, and sideroblastic anemia.^® Occasionally, until iron stores have been completely exhausted and macrocytes are found in chronic obstructive pulmonary additional iron depletion restricts iron to the erythron. FIGURE 8-4. Types of macrocytosis. (A) Macrocytes in film of patient with alcoholism and liver dis¬ ,2 ease. (From Bell A, Lofsness KG: A photo essay on red cell morphology. J Med Technol 3:85, 1986, with permissionj (B) Oval macrocytes in film of patient with vitamin B deficiency. Both xIOOO. 90 MORPHOLOGIC EVALUATION OF ERYTHROCYTES Iron deficiency is first apparent in biochemical iron stud¬ Some automated cell counters generate the red cell ies (Chap. 13). As anemia develops, Hb concentration is distribution width (RDW), which is reported to quantitate depressed, and red cells become more microcytic and hy¬ anisocytosis. The RDW is said to identify minor popula¬ pochromic. tions of microcytic or macrocytic cells^” that are not appar¬ Microcytes occur on the blood film when the MCV ent from the MCV, although the clinical significance of is below 80 fL. However, only a few microcytic cells may the RDW requires further study (Chap. 10).^^ not cause a decreased MCV. Significant numbers of micro¬ cytes are not produced until storage iron has been de¬ pleted for many weeks. SHAPE VARIATION— Microcytes with a diameter of 6 ^im or less are charac¬ POIKILOCYTOSIS teristic of iron deficiency anemia (Fig. 8-5). Inflammation Normal erythrocytes show little or no shape variation. may also cause a slight microcytosis. Decreased globin synthesis in j8-thalassemia (Chap. Variation only on the edges of films primarily is an artifact 15) results in a variable number of microcytic, hypochro¬ of preparation. mic red cells along with target cells. Because blood films The term used for variation in red cell shape is poikilo- in iron deficiency and thalassemia may be similar, special cytosis. Recognition of various shapes or poikilocytes on Hb determinations and family studies are needed for the the film is helpful in the differentiation of anemias. Exam¬ differential diagnosis. ples of poikilocytes characteristic of certain anemias in¬ Erythrocytes that are small, lack central pallor, and clude elliptical, sickled, fragmented, and spherical forms. appear to have an increased Hb concentration are seen in Generally a descriptive term of Greek origin is used to some hemolytic anemias. Such cells are called spherocytes. identify the poikilocyte. Poikdocyte shapes can sometimes Erythrocytes that are thinner than normal and have be explained by structural and biochemical changes in a colorless center are designated by the term leptocyte the membrane, an abnormal metabolic state in the cell, Hb (from the Greek word lepto, "thin”)- A leptocyte has an molecule abnormalities, an abnormal microenvironment, increased surface area that is out of proportion to the changes in the red cell's ability to deform, or red cell age. volume. Leptocytes may be normocytic or microcytic. Mi¬ Electron microscopy has greatly advanced our under¬ crocytic leptocytes are formed because of a lack of Hb, standing of the mechanism of poikilocyte production. as seen in severe iron deficiency. Small leptocytes may be seen in thalassemia and hemoglobinopathies such as Hb C, occasionally in sideroblastic anemia and obstruc¬ Poikilocytes Secondary tion of the bile ducts, and sometimes in cirrhosis and to Developmental Macrocytosis steatorrhea (fatty feces).^ (Oval Macrocytes) A markedly increased MCV (more than 125 fL) strongly Variation in Size (Anisocytosis) implicates megaloblastic erythropoiesis caused by vita¬ Correlated with Red Cell min B]2 or folate deficiency (Chap. 12). A nuclear matura¬ Distribution Width (RDW) tion defect in the early nucleated red cells of the bone marrow leads to development of macrocytes, which are Variation in red cell population size or diameter is termed mostly oval (oval macrocytes or macroovalocytes) (Eig. anisocytosis. To report anisocytosis the examiner should 8-4B). Even a few oval macrocytes are significant and see a mixture of normal cells with small or large cells, or suggest megaloblastic anemia. The cells appear well filled both. Anisocytosis should be estimated in a semiquantita- with Hb because of their increased thickness. Hb content tive manner; slight, moderate, or marked. If the variation increases as the cell increases in size, thereby forming a is primarily microcytes or macrocytes, or both, this should macrocyte that no longer has a central pale area. be reported also. Poikilocytes Secondary to Membrane Abnormalities Certain poikilocytes suggest hemolytic disorders and he¬ reditary or acquired conditions involving the red cell membrane.”'^®'®'®'^ SPHEROCYTES Spherocytes are rounded red cells that lack central pallor, show increased staining intensity, and usually have a smaller volume than a normal cell (Eig. 8-6). However, every spherocyte may not be truly spherical in vivo, and a slight concavity may be revealed with stereoscan mi¬ croscopy. Spherocyte diameter is approximately 6.2 to 7.0 FIGURE 8-5. Microcytic, hypochromic red cells in a patient with fim, and the thickness ranges from greater than 2.2 up to iron deficiency anemia. XI000. 3.4  Shape Variation—Poikilocytosis 91 Usually no more than 1% of the red cells in normal individuals are slightly elliptical.Ovalocytes or elUpto- cytes may be acquired in iron deficiency anemia, megalo¬ blastic anemia, and myelophthisic anemia, in which as many as 10% of the cells may be oval. Megaloblastic anemia is characterized by oval macrocytes (Fig. 8-4B), which may be 9 jxm or more in diameter and lack central pallor. Elliptocytes are also observed in thalassemia and sickle cell anemia. Hereditary elliptocytosis (Chap. 17) is characterized on the blood film by 25% to 90% elliptocytes, but it is not typically associated with hemolysis.^' The principal defect is considered to be in the cytoskeleton, with a decrease FIGURE 8-6. Spherocytes in film of patient with hereditary sphe¬ in the skeletal membrane protein band 4.1.’ An increased rocytosis. XI000. heat sensitivity of spectrin in some families with heredi¬ tary elliptocytosis has been reported.^^ The Life span of elliptocytes may be somewhat shortened in a few individ¬ Spherocytes may be caused by a hereditary or an uals; however, elliptocytes usually function normally. The acquired condition. Several molecular defects in mem¬ osmotic fragility is normal. brane proteins have been identified in hereditary sphero¬ cytosis (Chap. 17); spectrin deficiency has been found in many patients.”-^®'^^ Spherocytes are not easily deformed ECHINOCYTES AND BURR CELLS and therefore may lose their membrane by fragmentation Echinocytes (from the Greek echinos, "sea urchin") have during passage through the circulation. These cells be¬ evenly distributed, uniform-size blunt spicules or bumps come smaller and denser with increased Hb content and on their surfaces (Figs. 8-8A, 8-13). Echinocytes or cre- become less deformable with age. When the cell is de¬ nated red cells may be seen on films made from anticoagu¬ prived of membrane as it ages, it assumes the spherical lated blood that is several hours old, but such cells are shape. Spherocytes have a shortened survival time be¬ artifacts not normally present in vivo. Bessis^ states that cause they are sequestered in the spleen and hemolyzed.^^ crenation is caused by release of basic substances from The presence of spherocytes indicates a hemolytic glass slides that change the pH and transform the cells process because hemolysis results from a membrane ab¬ into echinocytes. In stored blood echinocytes may be nu¬ normality. The hallmark of hereditary spherocytosis is a merous because of depletion of ATP and biochemical spherocyte that is fairly uniform in size and density with abnormalities in plasma. Echinocytes formed in vitro can a decreased membrane surfaceivolume ratio. The MCV be reversed to normal shape, whereas those formed in may be normal or slightly decreased; the MCHC is often vivo cannot.'' Transformation of discocytes to echinocytes increased. Spherocytes show increased fragility when can be observed on a glass slide using a moist saline placed in increasing dilutions of hypotonic saline in the preparation of red cells in the presence of an elevated osmotic fragility test (Chap. 17). After splenectomy in (basic) pH.’' patients with hereditary spherocytosis, hemolysis de¬ In anemia associated with renal insufficiency (Chap. creases but spherocytes persist,’^ indicating that the ab¬ 18), some red cells acquire a membrane abnormality with normality involves the red cell membrane itself rather irregularly sized and unevenly spaced spicules.^^ Such than splenic damage to the cells. red cells are called burr cells (Figs. 8-8B, 8-13). The number Frequent causes of acquired spherocytosis are immu- of burr cells often increases as blood urea nitrogen (BUN) nohemolytic anemia secondary to autoimmune or isoim¬ increases. This membrane alteration is probably related mune antibodies, Heinz body hemolytic anemia, microan¬ to plasma chemical abnormalities. The spicules of burr giopathic hemolytic anemia, and hemolysis secondary to water dilution.” Banked blood stored for long periods of time develops spherocytes. Transfused cells are often spherical when viewed on a blood film and can be differ¬ entiated from the patient's cells. ELLIPTOCYTES AND OVALOCYTES Elliptocytes or ovalocytes are erythrocytes that have an elliptical or oval shape (Fig. 8-7). These cells result from hereditary or acquired conditions and range from egg- shaped or slightly oval to sausage, rod, or pencil forms.^^ With electron microscopy, Hb appears to be concentrated at the two ends of the cell, leaving a normal central area of pallor.”'^^ Late nucleated red cells in the bone marrow of pa¬ O tients with elliptocytosis are not elliptical except in rare FIGURE 8-7. Elliptocytes in film of patient with hereditary ellipto¬ cases of hereditary elliptocytosis. cytosis. XI000, 92 MORPHOLOGIC EVALUATION OF ERYTHROCYTES FIGURE 8-8. (A) Echinocytes or crenated cells in film of normal peripheral blood. (B) Burr cells in film of patient with uremia. Note resemblance to echinocytes. Both XI000. cells are usually reversible, as the cells can be induced to Acanthocytes have been observed in alcoholic cirrho¬ revert to normal shape. sis with hemolytic anemia, malabsorption states, postsple¬ The differences between crenated cells (echinocytes) nectomy states, hepatitis of newborns, pyruvate kinase and burr cells may be minimal and not always recogniz¬ deficiency, and disorders of lipid metabolism.^ Cells simi¬ able. Crenated cells with uniform blunt spicules represent lar to acanthocytes have been named spur cells in severe an artifact that is evident in practically every cell in the hemolytic anemia associated with cirrhosis and in meta¬ thin portion of the film and should not be reported. In static liver disease because of their sharp points.^^'^® contrast, burr cells may be distinguished by their irregu¬ Increased numbers of acanthocytes have been re¬ larly sized spicules and variable number in different mi¬ ported in a rare congenital syndrome called abetalipopro- croscopic fields and should be reported. A burr cell has teinemia (Chap. 17), which is characterized by mild hemo¬ also been called an echinocyte by several hematologists lytic anemia, retinal degeneration, and steatorrhea.^-^^ because of its membrane irregularities. STOMATOCYTES ACANTHOCYTES Stomatocytyes on a fixed and stained film have an elon¬ Acanthocytes (from the Greek word acantho, "thorn" or gated or slitlike area of central pallor (Fig. 8-10) instead "spike") are small, densely stained red cells that are no of the usual circular form. These cells may be hereditary longer disc shaped and have a few irregularly spaced, or acquired. The Greek word stoma means mouth. Stoma- pointed spicules or thornlike projections of various tocytes are so named for their mouth-shaped central pal¬ lengths and widths over their surfaces (Fig. 8-9). The lor. These cells appear bowl shaped in a moist preparation spicules may appear clublike. Acanthocytes may be ac¬ and by stereoscan microscope.^ quired or inherited and are smaller than normal red cells Blood films from normal individuals may demon¬ because they are becoming spheroidal. Generally acan¬ strate a few stomatocytes, but stomatocytes are usually thocytes have fewer, more irregular, and more blunted observed in patients with alcoholism, cirrhosis, obstruc¬ points than burr cells. Also, unlike burr cells, acanthocytes tive liver disease,” and Rh null disease.^* These cells also cannot be induced to regain a normal shape. Acanthocytes may occur as artifacts of blood film preparation. may be caused by changes in the ratio of plasma lipids Hereditary stomatocytosis is characterized by numer¬ (lecithins and sphingomyelins).“ ous stomatocytes, but anemia is usually mild.^^ One of FIGURE 8-9. Acanthocytes. As s sen in film of patient with mi- FIGURE 8-10. Stomatocytes in film of patient with hereditary sto¬ croanglopathic hemolytic anemia XI000. matocytosis. XI000.  Shape Variation—Poikilocytosis 93 the suggested consequences involves a membrane defect SCHISTOCYTES that results in high cellular sodium and low potassium When a red cell attempts to pass between fibrin strands,^^ content (Chap. 17). The heterogeneous clinical picture altered vessels, or damaged heart valve prostheses,®^'^ it results from an abnormal sodium to potassium transport may be cleaved and fragmented and become a schistocyte ratio and a greatly increased rate of active cation trans¬ (Figs. 8-12A and B, 8-13). The erythrocyte trying to port.*^ Because of the shape of the red cell and the some¬ squeeze through an opening half its diameter becomes what impaired deformabiUty, stomatocytes may be re¬ stretched and develops a blister (Fig. 8-12C) because of tained in the spleen. the shear stress of the flowing blood. When this cell passes through the spleen, it is fragmented into two pieces, and CODOCYTES (TARGET CELLS) the membrane is less deformable. Fragmented red cells do not survive long in the circulation.^^ Codocytes or target cells have a central area of Hb sur¬ Schistocytes (Greek word schistos, "cloven") or rounded by a relatively colorless ring and a peripheral schizocytes (Greek schizo, "split") result from membrane ring of Hb (Fig. 8-11). By scanning electron microscopy damage; they are not hereditary. Schistocytes include hel¬ the codocyte has a bell or tall hat shape and appears to met, triangular, and a variety of small, irregular shapes be thin walled and concave. A codocyte (Greek kodon, with a few pointed extremities. The finding of helmet and "bell") is also called a Mexican hat cell. This shape is fragmented cells is strongly suggestive of a microangio¬ always acquired. Codocytes appear when the membrane pathic hemolytic anemia or traumatic hemolytic anemia surface is increased after loading of the membrane with (Chap. 18).*^ Schistocytes occur in patients with severe cholesterol and phosphoUpids.'^ In other words, a target burns, renal graft rejection, glomerulonephritis, vasculi¬ cell is similar to a bag too large for its contents. Its greater tis, thrombotic thrombocytopenic purpura, and diffuse osmotic resistance (or decrease in osmotic fragility) is intravascular coagulation.^'” Schistocytes accompanying explained by the increase in surface to volume ratio. march hemoglobinuria most likely are attributable to me¬ Finding target cells in only one portion of the film chanical damage to the cells in the feet of individuals on suggests an artifact of film preparation. Fixing blood films long walking expeditions. in methanol before staining may help avoid this problem. In pathologic states, target cells are observed throughout SCHISTOCYTES AND KERATOCYTES the usual examination area. Target cells do not appear at the ends of a film where cells are flattened nor in thick A schistocyte with one or more hornlike projections has portions of the film. been identified as a keratocyte (Greek keras, "horn") (Fig. Codocytes are characteristic of thalassemia; hemoglo¬ 8-12D). These cells may or may not have a normal volume binopathies SS, CC, DD, EE, and S-thalassemia; obstruc¬ and usually no area of central pallor. A keratocyte is the tive liver disease; postsplenectomy state; and iron defi¬ result of an erythrocyte being caught on a fibrin strand, ciency anemia (Chaps. 13, 14, 15).” '^'^’ which could cut the cell in two. As the sides of the erythro¬ cyte are pushed against the fibrin strand, they tend to fuse together. When this cell escapes from the fibrin strand, it may have a vacuole-like area in the fused portion (this Poikilocytes Secondary to Trauma is known as a blister cell; Fig. 8-12C). This vacuole ruptures Erythrocytes may fragment and lyse when subjected to to form the keratocyte—a damaged red cell with horns. excessive physical trauma in the cardiovascular system. Keratocytes do not remain in circulation for more than a Intravascular hemolysis and shortened red cell survival few hours, as they are fragile.^ A keratocyte is a rare may result from severe trauma. The hallmark of hemolytic and interesting phenomenon. Some morphologists report anemia secondary to red cell fragmentation is the schisto- helmet cells, which actually look like a helmet, as kerato¬ cyte, which takes several forms. Other cells caused by cytes. trauma are included in this section. DACRYOCYTES (TEARDROPS) Dacryocytes (teardrops) have been so labeled because of their shape (Greek dakry, "tear") (Fig. 8-14). They may also be pear shaped with a blunt pointed projection and may be normal size, small, or large.^'“ If a red cell contains a rigid inclusion, such as a Heinz body, the portion with the inclusion cannot pass through small openings of splenic sinuses and thus remains behind. As the red cell squeezes through the small opening, it is stretched be¬ yond its ability to regain its original shape. Thus, a tear¬ drop or pear shape is created.^ Teardrop cells typically are observed in myelofibrosis with myeloid metaplasia (Chap. 35) because of the large size of the spleen. Other conditions with dacryocytes in¬ clude myelophthisic anemia, pernicious anemia, /S-thalas¬ FIGURE 8-11. Codocytes (target cells) in film of patient with liver semia, drug-induced Heinz body formation, tuberculosis, disease. xIOOO. and tumor metastasized to the marrow.^'^'^^ 94 MORPHOLOGIC EVALUATION OF ERYTHROCYTES I I 0 Hi FIGURE 8-12. Schistocytes. (A, B) In film of patient with thrombotic thrombocytopenic purpura. Note helmet, triangular, fragmented, and bizarre shapes. (C) Blister cell in film of patient with probable mi¬ croangiopathic hemolytic anemia. (D) Keratocytes (horn cells) in film of patient with microangiopathic hemolytic anemia. All XI000. I ! Multiple processes Moderate number Few processes per cell per cell processes per cell Membrane injury I I 1 1 Regularly spaced Irregularly spaced Irregularly spaced i' ! Blunt pointed Pointed Thorn-like Fragmented Similar length Variable length Spicules I i ' I Cell usually Cell usually Dense Dense normochromic normochromic Small cell Small cell Crenated Burr Acanthocyte Schistocyte Helmet (Echinocyte) Spiculated Fragment Spur FIGURE 8-13. Analysis of membrane irregularities in red blood cells.  Shape Variation—Poikilocytosis 95 FIGURE 8-14. Dacryocytes (teardrop cells) in film of patient with m FIGURE 8-16. Semilunar bodies (red cell ghosts) In film of patient vitamin B12 deficiency. xiOOO. with malaria. xiOOO. MICROSPHEROCYTES (see Protozoan Inclusions later in this chapter) and in AND PYROPOIKILOCYTES other conditions causing overt hemolysis. Microspherocytes (Fig. 8-15A) occur in severe burns as small, round cells that may be smaller than platelets. They are the result of thermal damage to the cell membrane.^^ Poikilocytes Secondary to Abnormal Another name for these round fragments is micro¬ Hemoglobin Content spherules. Poikilocytes can be diagnostic of a chronic hereditary A rare hereditary hemolytic anemia designated pyro- hemolytic anemia. Three types of poikilocytes are charac¬ poikilocytosis (Chap. 17) presents a striking picture of teristic of three abnormal hemoglobins: drepanocytes fragments and microspherocytes (Fig. 8-15B) associated (from Hb S), Hb CC crystals, and Hb SC crystals with heat sensitivity. The red cell abnormality probably (Chap. 14). is in the membrane protein spectrin (Chap. 17). These tiny, round, fragmented cells are greatly increased when blood cells are heated in vitro to 45°C, in contrast to normal DREPANOCYTES (SICKLE CELLS) red cells, which fragment around 49°C.^’ The mean diame¬ Drepanocytes (sickle cells) (Greek drepane, "sickle") have ter of the spherical fragments is approximately 2 to 3 ^im, been changed from the normal disc shape by the long and the MCV is extremely low (less than 60 fL).^^'® rod-shaped polymers of the inherited abnormal Hb S. A red cell does not appear sickled until it has lost its nucleus SEMILUNAR BODIES and has been fully hemoglobinized. Sickle cells are thin A semilunar body (half-moon cell; crescent cell) is a large, and elongated with pointed ends and are well filled with pale-pink staining ghost of a red cell—the membrane Hb (Fig. 8-17). They may be curved or straight or have remaining after the contents have been released (Fig. S, V, or L shapes.^^ This change is striking and irreversible 8-16). Semilunar bodies are as large as leukocytes and are secondary to permanent membrane damage by the poly¬ always acquired.^"* They are frequently seen in malaria merization of Hb FIGURE 8-15. Microspherocytes. (A) As a result of thermal damage in film of patient with severe burns. (B) As a result of heat sensitivity in film from patient with hereditary pyropoikilocytosis. (From Bell A, Lofsness KG: A photo essay on red cell morphology. J Med Technol 3:85, 1986, with per¬ mission.) 96 MORPHOLOGIC EVALUATION OF ERYTHROCYTES FIGURE 8-19. Hemoglobin SC crystals in film of patient with Hb FIGURE 8-17. Drepanocytes (sickled red cells) in film of patient SC disease. XIOOO. (From Bell A, Lofsness KG. A photo essay on homozygous for Hb S (sickle cell anemia). XI000. (From Bell A, red cell morphology. J Med Technol 3:85, 1986 with permission.) Lofsness KG: A photo essay on red cell morphology. J Med Tech- nol 3:85, 1986, with permission.) Typical sickle cells are observed in films from patients HEMOGLOBIN SC CRYSTALS with homozygous Hb S disease (Hb SS) but are not often Hb SC crystals within erythrocytes in Hb SC disease can seen in heterozygous Hb S (Hb AS; sickle trait) except be seen on searching. These dark-hued crystals of con¬ under unusual situations when there is low in vivo oxygen densed Hb distort the red cell membrane (Fig. 8-19). The tension. Therefore, morphology is not very helpful in the characteristic type of crystalline projection is often straight diagnosis of Hb AS. A few sickled cells may be seen in with parallel sides and one blunt, pointed, protruding end the abnormal Hb SC, Hb S-jS-thalassemia, Hb C-Harlem, ("Washington monument" shape).^ Another erythrocyte and Hb S-Memphis disorders. typical in Hb SC disease contains multiple crystals that protrude in different directions as finger-like projections HEMOGLOBIN CC CRYSTALS from a common crystalline center (Fig. 8-20). Intraerythrocytic Hb CC crystals in homozygous C (Hb Hb condensed in one portion of the cell often is ac¬ - CC) disease tend to be hexagonal with blunt ends and companied by relative pallor in the opposite portion. In darkly stained (Fig. 8-18). These angular crystals form occasional elongated cells, crystals form at opposite poles, - within the cell membrane when Hb C crystallizes, often leaving a hypochromic area in the center. Another feature leaving the remainder of the cell relatively Hb free and is the bent or curved cellular shape caused by polymers - colorless (Fig. 8-20). Frequently, the cell membrane is not of soluble Hb consisting of Fib S factoids mixed with Hb visible, and the crystal appears to be free. At times, several C crystals. smaller CC crystals form within the red cell.^^ Diggs and BelF reported intraerythrocytic crystals in Crystals of Hb CC are not observed in every patient 70% of the blood films from 60 cases of electrophoretically with electrophoretically proven Hb CC and in most in¬ proven Hb SC disease. The incidence of intracellular Hb stances are seen only after searching. Actually, the crystals SC crystals was found to be 0 to 23 per 1000 red cells. are more frequent after splenectomy. Crystals are not seen in Hb C trait (Hb AC). Finger-like projection(s) Hexagonal crystal ("Washington usually elongated monument") I I i Crystal protruding Crystal formed within cell membrane cell membrane Projecting end blunt Both ends blunt Parallel sides to projection I Parallel sides to crystal FIGURE 8-18. Hemoglobin CC crystals in film of patient with ho¬ Hb SC crystal Hb CC crystal mozygous Hb C disease. xiOOO. (From Bell A, Lofsness KG: A photo essay on red cell morphology. J Med Technol 3:85, 1986, FIGURE 8-20. Analysis of hemoglobin crystals in red with permission.) blood cells.