Hematology I - SCIE2020 Harmening Chapter 5 - PDF

Hematology I (SCIE2020) Harmening - Chapter 5 : Part A (5th Ed) Harmening - Chapter 4 : Part A (6th Ed) Evaluation of RBC Morphology + Intro to Platelet and WBC Morphology  O...

Hematology I (SCIE2020) Harmening - Chapter 5 : Part A (5th Ed) Harmening - Chapter 4 : Part A (6th Ed) Evaluation of RBC Morphology + Intro to Platelet and WBC Morphology  OBJECTIVES  4.7 List the steps in the performance of a peripheral blood smear examination.  4.8 Identify normal red blood cell morphology on a peripheral smear.  4.9 List the terms referring to abnormal red cell distribution, variation in red cell size, and variations in red cell color/hemoglobin content, being able to identify each abnormality on a peripheral smear and specify the particular clinical conditions associated with these abnormalities.  4.10 Define anisocytosis and poikilocytosis and list clinical conditions in which they may be reported.  4.11 Define the terms normochromic, hypochromic, microcytic, and macrocytic as they relate to red cell indices.  4.12 Correlate red cell indices with red cell morphology and the diagnosis of anemia.  4.13 Define the following terms: target cells, spherocytes, ovalocytes, elliptocytes, stomatocytes, and be able to identify these cells on a peripheral smear.  4.14 List diseases that may show fragmented red cells and describe their pathophysiology.  4.15 Describe the most common red blood cell inclusions and their composition, relating each inclusion to clinical conditions in which they may be found.  2.19 State the principle of the erythrocyte sedimentation rate (ESR) procedure  2.20 List errors that could occur in the performance of the erythrocyte sedimentation rate (ESR) procedure  2.21 List factors affecting erythrocyte sedimentation rate (ESR) (immunoglobulins, microcytes, MORPHOLOGY OF ERYTHROCYTES Examination of a correctly prepared and stained peripheral blood smear is of utmost importance in Hematology!  3 Introduction  This chapter is a guide for interpretation of red cell, platelet, and white cell morphology by first defining what is considered normal. At this time, emphasis is on red blood cells.  Consider basic assessment techniques of the cellular morphology, with particular emphasis on recognizing a distinct red blood cell morphology and relating it to the clinical condition.  We’ll look at various morphologies and physiologic mechanisms to get an understanding of an abnormality and how it relates to different disease states.  Included are descriptions of various red blood cell morphologies to help with recognizing and correlating the blood morphology to the clinical pathology and abnormal results. Examination of the Peripheral Blood Smear  A blood smear examination may be performed for a variety of reasons:  It may be requested by the physician in response to perceived clinical features or to an abnormality discovered in a previous CBC.  The examination may also be initiated by the technologist as a result of an abnormality in the CBC or in response to a flagged result reported from the hematology analyzer. A flagged result is an indication that a particular result has not met established laboratory criteria and must be reviewed  All laboratories should have a documented protocol/established guidelines for smear review.  The protocol may be derived from studies performed in the hospital/institution or may be based on nationally recognized standards.  A careful and thorough examination via light microscopy in the optimal area (on a well made, well stained peripheral smear) provides important and valuable information about morphology (normal or abnormal).  It is used to detect or verify abnormalities and subsequently may provide the physician with information to make a diagnosis.  Helpful in the diagnosis of various forms of anemia (aka. abnormal red cell morphology).  The examination of the blood smear should include evaluation of:  RBC morphology  WBC morphology  PLT morphology  To evaluate the smear thoroughly the technologist should review at least 10 high-power (100X) oil immersion fields (OIF).  The red cell morphology evaluation should include examination for deviations in size, shape, distribution, concentration of hemoglobin, color, and the appearance of RBC inclusions.  White blood cell morphology should consist of differentiation of the white blood cells and their overall appearance including nuclear abnormalities, cytoplasmic abnormalities, and the presence of any inclusions that may denote a disease process.  Platelet morphology / estimates should be verified and the smear should be reviewed for platelet shape and size abnormalities and for clumping.  When abnormal morphology is identified on the smear, the technologist must determine if the abnormality is possibly artifactual (and not pathological).  Aka. Abnormal due to user error, not a true indicator of disease.  Example: Refractile artifacts may be the result of water contamination (humidity) and should not be confused with red cell inclusions.  Crenated cells (echinocytes) may also be artifacts if practically every cell in the thin portion of the film has a uniform spicules in the membrane. This occurs when samples are left in EDTA anticoagulant for > 4-hours. The following describes the necessary steps in the examination of the peripheral blood smear Reminder: Also refer to your lab manual  Low-Power (10×) Scan 1. Determine the overall staining quality of the blood smear. 2. Determine if there is a good distribution of the cells on the smear. Scan the edges and center of the slide to be sure there are no clumps of RBCs, WBCs, or platelets. Scan the edges for abnormal cells. 3. Find an optimal area for the detailed examination and enumeration of cells. The RBCs should not quite touch each other. There should not be areas containing large amounts of broken cells or precipitated stain. The RBCs should have a graduated central pallor. High-Power (40×) Scan  1. Determine the WBC estimate. ** The WBC estimate is performed under high power (40× magnification). WBCs are counted in 10 fields and then the average is calculated. ** 2-6 WBCs/hpf should correlate with a normal adult white cell count. Oil Immersion (100×) Examination  1. Perform a 100 WBC differential count.  2. Evaluate the RBCs for anisocytosis, poikilocytosis, hypochromasia, polychromasia, and inclusions.  3. Perform a platelet estimate and evaluate platelet morphology.  Count the number of platelets in 10 OIFs.  Calculate the average number of platelets  Multiply by 15 if the slide was prepared by an automatic slide maker  Multiply by 20 for all other blood smear preparations (manual) Normal RBC  Reddish-pink colour (Wright stained smear)  Size is ~ 6 - 8 µm in diameter  ~ 5% variation in size is normal  Average volume is 90 fL (MCV)  A normal RBC is approximately the size of the nucleus of a small lymphocyte  It’s main function is formation of Hgb to carry O2 to tissues / organs 13  The Normal Red Blood Cell  Mature RBCs lack a nucleus and organelles, and yet all components necessary for survival and function are present.  It is described as a biconcave disc  It has a life-span of ~ 120 days.  On a Romanowsky (i.e., Wright’s stain, Wright-Giemsa stain) stained blood smear, this mature red cell has a reddish-pink appearance.  The RBC has an average diameter of 7 to 8 µm and an average volume of 90 fL.  The area of central pallor is approximately 1/3 the size of the cell (2 to 3 µm in diameter) and the size variation of red cells from a normal patient is approximately 5%.  The primary function of the red cell is the transportation of O2 to the tissues of the body and transportation of CO2 back to the lungs for expulsion.  Fundamental to the red cell is the formation of hemoglobin, which is ultimately responsible for binding the oxygen molecule for transport. The Normal Red Blood Cell  The oxygen-carrying capacity of each erythrocyte is dependent on the production of adequate amounts of functional hemoglobin.  Also fundamental to the red cells functionality is the maintenance of the cellular membrane. The red cell membrane is composed of equal weighted portions of lipids and proteins and is responsible for sustaining a constant surface-to-volume ratio.  Maintaining the integrity of this membrane is essential to the cells shape and deformability which allows the RBC to traverse through the microvasculature of the body. An alteration of this membrane may result in the inability of the red cell to function efficiently and ultimately may lead to the cell's early demise/shorten lifespan. Assessment of RBC Abnormality (Harmening p. 96) Two criteria (2) you should ask yourself when examining a blood smear for abnormalities: 1. Is the abnormality seen in every field? 2. Is the morphology pathological, and not artificially induced? (i.e. Artefact) 16 Med Lab Technologist then makes an assessment of:  Size variation (Anisocytosis)  Shape variation (Poikilocytosis)  Color variation (Degree of hemoglobinization) Examine the stained smear (film). Look at least 10 oil immersion fields (100X). 17 Assessment of Red Cell Abnormality  A well-stained and well-made blood smear with an even distribution of RBCs in the area to be examined (i.e. body) is essential for any peripheral blood smear review.  Make a general assessment of whether the morphological abnormality is due to shape change (poikilocytosis) or size change (anisocytosis) or a change in color.  Most assessments of anisocytosis are performed while considering the red cell indices and the red cell distribution width (RDW) values obtained from the hematology analyzer. When examining a stained smear, the technologist considers the percentage of cells that vary in size in at least 10 OIFs.  For example, if the mean corpuscular volume (MCV) was 65 fL (80 to 100fL is normal for adults), the technologist would expect to see a large percentage of small cells.  If the MCV were 105 fL, the technologist would expect to see primarily larger cells.  Battlement pattern Figure 5-2 Normal red blood cells.  Changes in Erythrocyte Size Normocytic The normal erythrocyte varies slightly in size (about 5% variation) ** MCV = 80 - 100 fL Microcytic ** MCV < 80 fL Macrocytic ** MCV > 100 fL Reticulocyte Macrocytes should be evaluated for:  Shape (oval versus round)  Color (red versus blue)  Pallor (if present) 20  RBC inclusions Anisocytosis Variation in cell size. It should not be confused with:  Normal erythrocyte size variation (5%)  Increased polychromasia  A dimorphic blood picture (“di” = “two”) Anisocytosis may be graded according to a scale: 1+, 2+, 3+, 4+ See Harmening, p. 97, Table 5-2 Grading Scale for Red Cell Morphology and Fig. 5.3 21 Harmening p. 97  The majority of laboratories use either qualitative remarks (“few” or ”marked”), or a numerical grading (1 + to 4+) based on percentage of variation and to describe the type of cell or cells that have caused the variation from the normal.  With this method, a med lab technologist can present to the physician a series of ratings that can translate to a visual impression of a patient's peripheral smear.  This assessment is often critical to the diagnosis (!)   Note that the assessment of RBC morphologic abnormalities remains a manual task that is somewhat subjective, and it is important that laboratories establish guidelines based on their own patient and physician population.  It is essential to patient care that the laboratory have similar guidelines/interpretations of the results reported for all RBC morphology. Variations in Red Cell Distribution Normal Distribution  The area of smear that is reviewed for morphologic abnormalities is of the utmost importance.  The area to be reviewed should be in the thin portion (body) of the smear where the red cells are slightly separated from one another or at most, barely touching, with no overlap.  The thin area should represent at least one-third of the entire film. The technologist should avoid the thicker portion (head) of the slide where cells are overlapping and the edges of smear where cells may be artifactually distorted in size, shape, and color. An exception is to be made when scanning for platelet clumping. Abnormal Distribution Variations in RBC Distribution Rouleaux formation cylindrical column “Stacked coin” formation related to increased plasma proteins possibly due to delay in spreading blood, smear too thick Saline will disperse rouleaux. Harmening p. 98, fig. 5.5; Anderson’s Atlas p. 28; 2 nd Ed p;26 Autoagglutination clumps of RBCs formed due to antigen-antibody reaction may be seen in cold antibody syndromes such as Paroxysmal Cold Hemoglobinuria agglutination occurs at room temperature; if agglutination is due to cold agglutinins, clumps may be dispersed by warming the specimen 26 Harmening p. 98, fig. 5.4; Anderson’s Atlas p. 27;2 nd Ed p.25 AGGLUTINATION  Agglutination is an aggregation of red cells into random clusters or masses.  It is the result of an antigen-antibody reaction within the body, and in cases of auto-agglutination, the reaction is actually with the patient's own cells and the patient's serum or plasma.  Such is the case with cold antibody syndromes, for example, Cold Agglutination Disease (CAD) and Paroxysmal Cold Hemoglobinuria (PCH) – We will learn about these syndromes later  AGGLUTINATION  Occurs at room temperature during sample preparation and appears as interspersed areas of clumping throughout the peripheral smear. The use of saline will not disperse these agglutinated areas; however, warming the sample to 37°C helps to break up the agglutinins, allowing for the possibility of normal slide preparation for morphology review.  The MCHC and MCV from these specimens are usually falsely elevated in response to the agglutinin formation. Other forms of autoagglutination may also occur spontaneously but are more likely to be seen in connection with certain hemolytic anemias, atypical pneumonia, staphylococcal infections etc.  Agglutination is not to be confused with rouleaux (!) Figure 5-4 Note the agglutination on the smear from a patient with cold agglutinin disease (CAD). ROULEAUX  Rouleaux is a condition in which red cells appear as stacks of coins on the peripheral smear. The stacks may be short or long, but regardless of the length, the red cells appear stacked on one another.  These stacks are rather evenly dispersed throughout the smear. Rouleaux formation is the result of elevated globulins or fibrinogen in the plasma, where the red cells have been more or less “bathed” in this abnormal plasma which gives them a sticky consistency. This lowers the zeta (ζ) potential, thus facilitating the stacking effect. The use of a saline dilution of the serum disperses rouleaux.  Rouleaux formation correlates with a high erythrocyte sedimentation rate (ESR). ROULEAUX  Rouleaux is seen in patients with hyperproteinemias, such as multiple myeloma (MM) and Waldenstrom’s Macroglobulinemia (WM).  It may also be seen in chronic inflammatory disorders, and some lymphomas. It is important to note that in cases of severe rouleaux it may be impossible to evaluate cell size or shape.  Peripheral smears reviewed in the thick portions of the smear and entire smears made too thick may appear to exhibit rouleaux. This is considered artifactual and should not be reported until it is verified in the thin portion of the smear or a new slide is prepared. Figure 5-5 Peripheral blood showing marked rouleaux formation. Note the “stacked coin” appearance of the red cells. Agglutination Rouleaux 33 Erythrocyte Sedimentation Rate (ESR) The ESR measures the setting of erythrocytes in diluted human plasma over a specified period. The distance that the red cells fall during this time is the erythrocyte sedimentation rate and is reported in mm/hour. The ESR test is NON-SPECIFIC – It doesn’t indicate one, definitive disorder or disease. It can also be affected by age, gender, age and other factors. Phases of Sedimentation : Formation (0 – 10 min)  Rapid Fall (10 – 40 min)  Packing (50 – 60 min) Normal ESR Reference Range: Males: 0 - 10 mm/hr Females: 0 - 20 mm/hr Increased ESR Decreased ESR Various Factors * Rouleaux * Polycythemia That May Affect the / agglutination ESR * Increased immunoglobulins * Increased albumin (proteins) * Newborns (HgbF) * Anistocytosis, such as acanthocytes, sickle cells, spherocytes, etc. C-Reactive Protein (CRP)  C-reactive protein (CRP) is a protein made in the liver.  High levels of CRP are indicators of inflammation – like an ESR test  CRP testing is considered SEMI-SPECIFIC for inflammatory conditions:  System Lupus Erythromatosis (Lupus)  Coronary artery disease  Liver disease / liver inflammation  Inflammatory Bowel Disease (IBD)  Chrohn’s Disease  Bacterial or viral infections  CRP is completed on automated chemistry analyzers in ~ 15-mins; CRP testing is faster than ESR testing, but is often more expensive.  There is a “high sensitivity CRP” (hsCRP) test is considered SPECIFIC for heart disease and stroke; This test can detect CRP in lower levels than the standard CRP test. Serum Viscosity Test  A test that is SPECIFIC for identifying hyperviscosity and/or hyperglobulinemia o “hyper” = increased / many o “globulin” = protein o “-emia” = of the blood  The viscosity of a patient’s sample is compared to water; A normal serum viscosity in a healthy adult is usually 1.5 compared to water.  Aka. Serum is very similar to water, with a slight increase in viscosity   Abnormal clinical condition with an increased serum viscosity include: o Waldenstrom's macroglobulinemia (increased IgM proteins) – MOST COMMON! o Multiple myeloma (increased IgG proteins) o Polycythemia (increased RBCs), and others.  Rouleaux and/or agglutination on a peripheral blood smear may indicate that hyperviscosity Variations in RBC Size (ANISOCYTOSIS) Anisocytosis  Any significant variation is size is known as anisocytosis.  This size variation is frequently found in the leukemias and in most forms of anemia. The severity of the variation should also correspond to an increased RDW.  Anisocytosis results from abnormal cell development, and typically results from a deficiency in the raw materials (i.e., iron, vitamin B 12, folic acid) needed to manufacture them or by a congenital defect in the cell's structure.  Cell size may deviate, from measuring smaller than the normal 7 µm, to being larger than normal. The terms used to describe these abnormalities are microcyte (≤6 µm) and macrocyte (≥9 µm).  These terms are used in conjunction with the terms microcytosis and macrocytosis and should also correlate with the red cell indice results.  Anisocytosis is graded in most institutions as 1+ to 4+. Source: Harmening Figure 5-6 Note the different size (anisocytosis) and shape (poikilocytosis) of the red cells. Compare the largest (macrocytic) cell below the arrow in the center of the field with the smaller (microcytic) cells. Figure 5-3 Normal and abnormal red blood cell morphology.  Normocytes  The average size of the erythrocyte is indicated by the measurement of the MCV, a result generated by the automated hematology analyzer.  The MCV is considered an integral part of a CBC. Observation of red cell morphology on the blood smear provides a quality control check on the electronic MCV, as well as the other two red cell indices:  Mean Corpuscular Hemoglobin (MCH)  Mean Corpuscular Hemoglobin Concentration (MCHC).  A “normal” MCV would correspond to the MCV reference range : 80 to 100 fL.  Subsequent review of the blood smear should yield no significant size variation from the normal 7- to 8-µm red cell. This scenario is referred to as normocytic and the red cells are referred to as normocytes.  This information would prove useful to the physician in the diagnosis of anemia.  Normocytes EXAMPLE: A normal MCV (80- 100FL) and a high RDW (> 14.5%), the med lab technologist would expect to see a mixture of large and small cells.  This scenario is referred to as a di-morphic population (“di” = “two”)  A di-morphic population is often the result of a recent blood transfusion or possibly the patient may be in the recovery stages of anemia. Patient history plays an important role in this situation. Macrocytes  Macrocytes are cells that have an MCV of greater than 100 fL.  Anemias associated with these cells are referred to as macrocytic. These cells may appear in the peripheral circulation by several mechanisms.  One mechanism is impaired deoxyribonucleic acid (DNA) synthesis, which results in megaloblastic erythropoiesis leading to a decreased number of cellular divisions, and consequently a larger cell. This form of erythropoiesis produces a megaloblastic anemia and may be the result of B12 or folate deficiency, chemotherapy, or any process producing a nuclear maturation defect. (We will learn more about this).  Macrocytes with an oval shape (macro-ovalocytes), neutrophilic hypersegmentation, as well as MCV values exceeding 120 fL are typically seen in this type of anemia. Macrocytes  The most common cause of non-megaloblastic macrocytosis is accelerated erythropoiesis which results from conditions such as acute blood loss or alcoholism.  The cells are released prematurely from the marrow, are non-nucleated, and appear larger than a mature erythrocyte.  On a Wright-stained smear the cells will appear as round polychromatophilic macrocytes and on a supravitally (i.e., new methylene blue) stained smear they appear as reticulocytes.  Neutrophilic hypersegmentation is not typically seen in this form of macrocytosis.  Macrocytosis may result from other conditions, such as hypothyroidism and various bone marrow disorders, as well as occur in neonatal blood, post-splenectomy, and in cases where excess plasma cholesterol may be taken up by the red cell which subsequently leads to an increase in the surface area of the cell. However, this last mechanism may possibly not be reflective of a “true” macrocytosis (Example: Obstructive liver disease). Microcytes  A microcyte is a small cell having an MCV of less than 80 fL.  Anemias associated with microcytes are said to be microcytic. The hemoglobin content of these cells may be normal to decreased. A consequence of any defect that results in impaired hemoglobin synthesis may produce a microcytic, hypochromic (MCHC 360g/L; 36% and may be seen in the peripheral smears of patients with hemolytic anemias, including hemolysis caused by burns.  It is reported in terms of the cell abnormalities resulting from the increased volume of hemoglobin and the decreased surface area.  The cell produced from these phenomena appears as a solid reddish- orange disc with no central pallor and is referred to as a spherocyte. Polychromasia  When RBCs are delivered to the peripheral circulation prematurely, their appearance in the Wright-stained smear is distinctive.  These red cells are described as polychromatophilic (diffusely basophilic) and are gray-blue in color and usually larger than normal red cells fig 5-10.  The basophilic color of the red cell is the result of the residual RNA involved in hemoglobin synthesis.  Polychromatophilic macrocytes, as seen on a Wright's stained smear, are actually reticulocytes; however, the reticulum cannot be visualized without supravital staining. Figure 5-10 Note polychromasia in the cell with the arrow. Variations in RBC Shape (POIKILOCYTOSIS) Poikilocytosis  Poikilocytosis is the term used to describe variation in RBC shape.  Normal erythrocytes vary only slightly from the concise round shape of a biconcave disc, so even a slight variation in significant numbers may prove to be important.  These poikilocytic cells may take on such peculiar shapes as teardrops, pencils, and sickles. The differential diagnosis of anemia cannot be determined from a reported poikilocytosis. The term should be used in conjunction with more descriptive terminology which would specify the particular morphological abnormality observed.  Examples of specific poikilocytes are:  Sickle cells, which result from abnormal hemoglobin  Spherocytes, which result from a red cell membrane abnormality, as many of the poikilocytic cells do. The differential diagnosis of some forms of anemia may be determined by identification of a specific morphological abnormality.  The term poikilocytosis refers to the entire red cell morphology in the scanned area of a peripheral smear and is graded as 1+ to 4+ (See Table 5-2)  The term “poikilocytosis” as a “catch all” phrase for abnormal red cells and in lieu of grading the smear for poikilocytosis opt only to grade the specific types of morphologically abnormal cells seen.  In these cases the particular cells may be reported in terms of:  Few = 1+  Moderate = 2+  Many = 3+  Marked = 4+  Spherocytes  Spherocytes have a reduced surface-to- volume ratio that results in a cell with no central pallor.  Because of their density (intense color) and smaller size, they are easily distinguished in a peripheral smear. Their shape change is irreversible and may also be seen as microspherocytes. NOTE: Spherocytes = Smaller, darker, denser, rounder   Spherocytes  Considered the most common form of the erythrocyte morphological disorders stemming from an abnormality of the cell membrane.  May be hereditary or acquired and may be produced by a variety of mechanisms affecting the red cell membrane.  Perhaps the most detailed mechanism for sphering is the congenital condition known as Hereditary Spherocytosis (HS).  This is an inherited, autosomal dominant condition and is due to a deficiency of, or a dysfunction in, the membrane proteins spectrin, ankyrin, band 3 and/or protein 4.2. Spherocytes  The membrane cytoskeleton is dependent on these particular proteins to maintain the shape, deformability, and elasticity of the red cell.  The deficiency and/or dysfunction of any one these membrane components will destabilize the cytoskeleton, resulting in abnormal red cell morphology and a shorter lifespan for the affected red cells in circulation.  Spherocytes  Spherocytes are typically seen in large numbers in peripheral smears from these patients.  Premature destruction of these abnormal erythrocytes in the spleen may produce a mild-to-severe hemolytic anemia, depending on the severity of the abnormality. Spherocytes  Erythrocytes from patients with hereditary spherocytosis (HS) have a mean influx of sodium (Na+) that is twice that of normal cells (!)  Because these spherocytes have increased ability to metabolize glucose, they can handle the excessive intracellular sodium while in the plasma, but when they reach the microenvironment of the spleen, the active–passive transport system is unbalanced with increased sodium and decreased glucose resulting in swelling and hemolysis of these cells.  We will discuss Osmotic Fragility later  Spherocytes 73 Discussed last lecture 74 Figure 5-13 Note the spherocyte at arrow in a blood smear from a patient with hereditary spherocytosis. Source: Harmening: Figure 5-14 Correlation of spherocytes to pathologic processes.  The acquired forms of spherocytosis share the mutual defect with Heritidary Speherocytosis (HS) in that there is a loss of membrane.  Also, in the normal aging process of red cells - they gradually lose their functionality through loss of cellular lipids, proteins, etc.; thus, spherocytes are produced as a final stage before senescent red cells are detained in the spleen and trapped by the Reticuloendothelial System (RES).  This natural process does not typically result in anemia.  Another mechanism of producing spherocytes that may result in a mild to severe anemia is Autoimmune Hemolytic Anemia. (AIHA)  The coating of the red cells with antibodies and the detrimental effect of complement activation results in the membrane loss of cholesterol accompanied by a loss of surface area without hemoglobin loss producing spherocytes.  The reduced surface-to-volume ratio of all spherocytes renders them abnormally susceptible to osmotic lysis; consequently, they have an increased osmotic fragility.  Hemolysis is known to result from membrane abnormalities; therefore, other hemolytic processes may also produce spherocytes.  They may also be seen as microspherocytes in the peripheral smears of burn patients.  Harmening Fig. 5-14 (a previous slide) lists the more common pathologic conditions in which spherocytes are seen. Target Cells (Codocytes)  Target cells appear on the peripheral blood as a result of an increase in RBC surface membrane.  Their true circulating form, as seen with an electron microscope, is a bell-shaped cell.  The name ”codocyte” is from the Greek word ”kodon” which means bell. Target Cells (Codocytes)  In air-dried smears, however, they appear as “targets,” with a large portion of hemoglobin displayed at the rim of the cell and a portion of hemoglobin that is central, eccentric, or banded see fig 5-11.  As the name implies, the cell actually resembles a target and is sometimes referred to as a “bull's eye” cell Target Cells (Codocytes)  The mechanism of targeting is related to excess membrane cholesterol and phospholipid and decreased cellular hemoglobin. Seen in patients with liver disease, in whom the cholesterol/phospholipid ratio is altered.  Mature red cells are unable to synthesize cholesterol and phospholipid independently. As cholesterol accumulates in the plasma, as seen in liver dysfunction, the red cell is expanded by increased membrane lipid, resulting in increased surface area.  Consequently, the osmotic fragility is also decreased.  Target cells are seen in many types of anemia see Harmening Fig 5-12; However, target cells are most prominent in the hemoglobinopathies, thalassemias and liver disease. Figure 5-11 Note the target cell at the arrow. Figure 5-12 Correlation of target cells to pathologic processes. Target Cell (Codocyte) 85 Discussed last lecture 86  Stomatocytes  The word stomatocyte is derived from the Greek word stoma, which means mouth.  They have a central pallor which is said to be slit-like or mouth-like on blood smears.  The abnormal morphology resulting in the stomatocyte is thought to be the result of a membrane defect.  Stomatocytosis is associated with abnormalities in red cell cation permeability that lead to changes in red cell volume, which may be either increased (hydrocytosis) or decreased (xerocytosis), or is some cases, near normal.  Hydrocytosis and xerocytosis represent the extremes of a spectrum of red cell permeability defects. The exact physiologic mechanism of stomatocytic shape is poorly understood and the molecular basis of this disorder is unknown.  Stomatocytes  Stomatocytosis may be acquired or congenital.  As with hereditary spherocytosis, stomatocytes are seen in significant numbers in the hereditary form known as hereditary stomatocytosis and in smaller numbers in the acquired form.  Many chemical agents can induce stomatocytosis in vitro (phenothiazine and chlorpromazine); however, these changes are reversible.  Stomatocytes are known to have an increased permeability to sodium; consequently, their osmotic fragility is increased.  We will discuss osmotic fragility test later in this course. Figure 5-15 Stomatocytes in peripheral blood. LAB THIS WEEK  Abnormal RBC Morphology  Part II (Poikilocytosis)   My Additional Notes Harmening Chapter 5  Part A  My Additional Notes Harmening Chapter 5  Part A