MORPHOLOGIC ABNORMALITIES OF THE ERYTHROCYTE

Transcription

1 MORPHOLOGIC ABNORMALITIES OF THE ERYTHROCYTE 68 Assignment: VIEW the RBC Morphology Slides located on Blackboard as you read/refer to the following pages regarding Morphologic Abnormalities of the Erythrocyte. Focus on the characteristics seen on the slides and the cause(s) and/or composition of each item. Complete the Day 3 RBC Morph Worksheet on page 74 of the manual. Directions for Blackboard online course: Select I, click on the purple Assignment button, click on Student Laboratory Material, select Day 3 RBC Morphology Slides. The evaluation of erythrocyte morphology is part of a differential. Careful examination of a well-made slide in the correct area is essential. Five RBC morphological features are evaluated on the Wright's stained blood smear....size, COLOR, SHAPE, INCLUSIONS, AND DISTRIBUTION. The NORMAL mature erythrocyte is a normocytic, normochromic biconcave disk that is not rigid and has no inclusions. RBC abnormalities are noted or quantitated (as per institution policy) and can give important CLUES to the cause of an anemia/disorder. The RBC indices should correlate with the findings observed on the blood smear. Note: When abnormalities are not reported, it is assumed that red cells are normal in appearance. A. VARIATIONS IN RBC SIZE Normal red cells have a mean size of 7u (range 6-8u), an MCV between fl (normocytes) and are uniform in size with an RDW < 14.0% (i.e., a homogeneous RBC population). ANISOcytosis refers to variations in RBC size...the presence of microcytes, normocytes and/or macrocytes with an elevated RDW > 14.0% (i.e., a heterogeneous RBC population). 1. Microcytosis - Microcytes are red cells smaller than 6u; MCV < 82.0 fl. Seen in anemias due to defective hemoglobin synthesis...iron deficiency, Thalassemias, Sideroblastic anemia; normal children. 2. Macrocytosis - Macrocytes are red cells larger than 8-9u; MCV > 98.0 fl. Seen in Megaloblastic anemias due to defective DNA synthesis..vitamin B 12 or folate deficiency; also liver disease, normal newborns and marked reticulocytosis^. ^Try to exempt red cells with polychromasia (blue tinge) from your grading of macrocytosis since reticulocytes are larger than mature red cells. 3. Anisocytosis - Heterogeneous/dimorphic RBC population with a high RDW and variable MCV. Seen post-transfusion, post-treatment for a deficiency, presence of two deficiencies and in the idiopathic type of Sideroblastic anemia. In this case, the MCV (a mean volume measurement) may be unreliable (falsely normal) making the evaluation of red cell size on the blood smear invaluable, as shown in the example below. AGE: 30Y SEX: F CBC & DIFFERENTIAL WBC COUNT 5.8 [ ] X10E3/uL RBC COUNT 3.16* [ ] X10E6/uL HEMOGLOBIN 10.3* [ ] g/dl HEMATOCRIT 30.5* [ ] % MCV 94.4 Unreliable [ ] fl MCHC 33.8 [ ] % RBC DISTRIB WIDTH 28.9* High [ ] % PLATELET 185 [ ] X10E3/uL (DIFFERENTIAL not shown) RBC MORPH Marked Anisocytosis Moderate Microcytosis Presence of two RBC sizes Marked Macrocytosis Invalid MCV (normal range)

2 B. VARIATIONS IN RBC COLOR A normal erythrocyte contains an amount of hemoglobin so only 1/3 of its diameter is empty in appearance (normochromia) Hypochromia - Hypochromia indicates the amount of hemoglobin in the erythrocyte is decreased and the central pallor area is greater than 1/3 the red cell diameter; the MCHC may be <32.0%. Seen in anemias due to impaired hemoglobin synthesis (often present with microcytosis). Consider the number of hypochromic red cells, as well as the degree of hypochromia in the RBCs. 2. Polychromasia/Polychromatophilia - Large red cells (8-10u) which display diffuse basophilia (blue tinge) due to residual RNA when stained with Wright's stain. The amount of polychromasia correlates with the number of circulating reticulocytes. Seen in a reticulocyte response following acute blood loss, initiation of corrective therapy or after red cell destruction; polychromatophilic red cells are commonly seen in normal newborns. C. VARIATIONS IN RBC SHAPE: POIKilocytosis refers to major deviations from the normal red blood cell shape (biconcave, discoid). Red blood cells must maintain their biconcave shape in order to deform or bend in microvessels, some as small as 0.3 microns in diameter in the spleen. Poikilocytes are damaged and/or rigid red cells. Many inherited and acquired conditions can cause a red cell to lose its shape and deformability. The cells become rigid and may be prematurely sequestered (by splenic macrophages) which can result in anemia if RBC lifespan is extremely shortened and marrow production of red cells can't keep up with red cell loss. There are nomenclature differences between authors concerning some types of specific poik. Certain poikilocytes are noted to occur as artifact during smear preparation (e.g., spherocytes, target cells). Specific poikilocytes: 1. Schistocytes (Schizocytes) - Damaged RBC (with loss of RBC membrane) which has resealed itself and circulates until removed by the RES. Occurs after impact of RBC with fibrin strands, trauma by artificial surfaces/diseased vessels, heat, toxins, or phagocytosis of RBC portions. Characteristics: RBC fragments which are irregular in size and shape, e.g. triangular, helmet, bite. Severe hemolytic anemias with intravascular hemolysis (due to intrinsic or extrinsic defects) Mechanical trauma - artificial heart valves Microangiopathic anemias - disseminated intravascular coagulation (DIC) Anemias due to infectious agents Clostridia toxins, malarial parasites Uremia due to kidney failure Thermal burns Heinz body anemias - G-6-PD deficiency 2. Spherocytes - This spherical shape is the hallmark of the red cell that has been damaged and is shortly to undergo lysis. Caused by membrane loss...occurs as normal RBCs age, as a result of a membrane defect in Hereditary Spherocytosis, heat damage or when phagocytosis of RBC portions containing inclusions or coated by complement and/or antibodies occurs. Characteristics: Spherical cells lacking a pallor area which are deeply colored and condensed looking in appearance. The red cell surface:volume ratio is decreased, with maximal amount of volume and least amount of cell surface area (commonly small cells). Spherocytes are rigid cells that are unable to deform in circulation; lifespan is shortened because they either rupture (lyse easily) or are sequestered/removed by the spleen. MCHC may be > 36.0%.

3 Hereditary spherocytosis, pre and post-splenectomy Warm autoimmune hemolytic anemias warm reacting autoantibodies HDN due to ABO incompatibility Normal newborns (small numbers) Infectious agents - Clostridia Post-transfusion of stored blood Thermal burns Heinz body anemias - G-6-PD deficiency Artifact Acanthocytes - Due to abnormal lipid metabolism (often increased membrane cholesterol). Characteristics: Spherocytic-type red cell with multiple, sharp spiny projections. No pallor area. These projections are irregularly spaced and may be of irregular thickness. Abetalipoproteinemia = Hereditary acanthocytosis Severe liver disease (spur cells) Post-splenectomy Chronic Granulomatous Disease with McLeod phenotype 4. Echinocytes - includes crenated and burr cells Characteristics: Red cells that have a pallor area and short, blunt, evenly spaced projections (crenated cells) or irregularly spaced sharp projections (burr cells). Crenated cells are reversible and typically the result of environmental changes, e.g., when blood is placed in hypertonic solutions (H 2 0 loss) or due to prolonged blood anticoagulation. Post transfusion of stored blood (crenated red cells) Liver disease Uremia Normal newborns Pyruvate kinase deficiency Artifact (crenated cells) 5. Target cells (Codocytes) - due to abnormal hemoglobin synthesis or abnormal lipid metabolism. Characteristics: When flattened, the hemoglobin is redistributed centrally and to the periphery of the cell with a lighter ring between the two. They appear to have excess membrane in comparison to hemoglobin content. Surface:volume ratio is increased; target cells tend to be resistant to lysis. Hemoglobinopathies presence of Hgb S or Hgb C Thalassemias Iron deficiency anemia Liver disease Post-splenectomy Artifact

4 6. Sickled cells (Drepanocytes) - Under decreased oxygen tension, Hgb S molecules will crystallize by polymerization and yield a fluid crystal with a sickle shape that is well-filled by hemoglobin. Sickle cells seen on the blood smear are irreversible. 71 Characteristics: These cells display an elongated shape with an irregular outline and sharp terminal projections, a curved sickle-like shape, or a boat-shape which can be confused with ovalocytes or pencil cells. Inherited presence of hemoglobin S (Hgb SS, Hgb SA in crisis ONLY, Hgb SC, Hgb S-Thal). 7. Hemoglobin C Crystals Characteristics: Condensed rod or bar-shaped crystals with blunt ends found in RBC's. Inherited presence of hemoglobin C (Hgb CC, Hgb SC; NOT Hgb CA). 8. Hemoglobin SC Crystals Characteristics: Bizarre shaped crystal; denser than sickle cells with fingerlike projections. Inherited presence of Hgb S and Hgb C (Hgb SC). 9. Ovalocytes/Elliptocytes Characteristics: Elongated, oval cells which tend to become more elongated as the cell ages. Elongation may be due to redistribution of hemoglobin or cholesterol to ends. Hereditary Ovalocytosis normocytic ovalocytes with normal hemoglobin content Artifact (if all in one direction) Small numbers on a normal smear Macrocytic ovalocytes in megaloblastic anemias called megalocytes Microcytic ovalocytes in iron deficiency and thalassemias May see pencil or cigar forms in severe iron deficiency which are red cells that have an exaggerated, elongated shape. One end may be irregular and pointed; can be mistaken for sickle cells. Pencils are usually thinner than normal and display hypochromia due to reduced hemoglobin content. Pencil forms should only be reported if the accompanying red cells are microcytic/hypochromic. 10 Teardrop cells (Dacrocytes, racquet forms) Characteristics: These cells display a single terminal projection which may be smooth or have an unfinished, jagged appearance. Megaloblastic anemia (large teardrops) Myelofibrosis (small teardrops) Thalassemia major Heinz body anemias 11. Stomatocytes (mouth or kiss cells) - Produced as a result of osmotic swelling through cation imbalance or due to a membrane defect in Hereditary Stomatocytosis. Characteristics: Unicave rather than biconcave; have slit-like pallor area rather than a rounded one. Osmotic swelling, decreased ph Hereditary Stomatocytosis including Rh null individuals Alcoholic cirrhosis, acute alcoholism, obstructive liver disease Artifact - shiny slit

5 D. RED BLOOD CELL INCLUSION BODIES 72 Normally, there are no red cell inclusions visible when the smear is stained with Wright's stain; any red cell inclusions are pitted out by the spleen as the red cells pass through. The presence of inclusions decreases red cell deformability and shortens red cell survival. RBC inclusions go in and out of focus; artifact is shiny/refractile and doesn t go in and out of focus. 1. Nucleated RBC's (nrbc's) counted while doing the differential; reported #NRBCs/100 WBCs. Characteristics: The nucleus is present in red blood cells. These are RBC's released into the blood before reaching maturity. They can be seen in any stage of maturation but are not staged. Increased erythropoiesis - high demand for red cells in severe anemias such as megaloblastic anemia, sickle cell disease, Beta thalassemia major Premature or newborn infants Rh disease of the newborn Erythroleukemia Leukoerythroblastic response due to marrow invasion 2. Howell-Jolly bodies - May represent nuclear instability; the casting off of chromatin material as a result of chemotherapy, rapid cell division, or impairment of normal nuclear maturation that is characteristic of megaloblastic anemias. Characteristics: Remnants of DNA/nuclear material in the cytoplasm after the nucleus has been extruded from the maturing red blood cell. They are dense, round, homogeneous bodies which are non-refractile and stain deep violet to black with Wright's stain; can be multiple. Severe maturation defects, particularly megaloblastic anemias *Post-splenectomy Leukemias (often post-therapy) In general, severe hemolytic anemias such as beta thalassemia major or sickle cell disease, in which the spleen becomes overwhelmed. 3. Pappenheimer bodies - Due to accelerated red cell mitotic division and/or impaired hemoglobin synthesis. Characteristics: Small dense blue granules at periphery of red blood cell (called a siderocyte) on a Wright's stained smear. These bodies are composed of iron and often degenerating ribosomes, mitochondria, and other remnants. Can be confirmed with Perl's Prussian blue iron stain. Sideroblastic anemia iron overload *Post-splenectomy In general, severe hemolytic anemias such as sickle cell disease, beta thalassemia major, megaloblastic anemia Transfusion-dependent anemias 4. Reticulocytes Characteristics: Large, immature red cells which still contain residual RNA that stains diffusely blue throughout the cell..seen as polychromasia on a Wright s stained blood smear. The RNA and basophilic substances can be precipitated out with supravital stains to definitively identify. Increased erythropoiesis, compensatory response to anemia.

6 5. Basophilic Stippling - Sign of disordered erythropoiesis and/or defective hemoglobin synthesis. 73 Characteristics: Punctate aggregations of basophilic RNA substance in the form of coarse blue granules seen throughout the red cell with Wright' s stain. Must differentiate basophilic stippling from diffuse polychromasia which may show faint dots in the red cell. Sideroblastic anemia, *especially lead intoxication Thalassemias In general, severe hemolytic anemias such as megaloblastic anemia, sickle cell disease 6. Cabot Rings - Thought to represent nuclear remnants. Characteristics: With Wright's stain, appear as fine ring-like reddish-violet structures, singly or double. Also in figures of 8, twisted and convoluted. Megaloblastic anemia Lead poisoning Dyserythropoiesis (myelodysplastic syndromes) 7. Heinz Bodies - Intracellular globin or hemoglobin precipitate that may result from denaturation of hemoglobin (preceded by oxidation and methemoglobin accumulation) OR may be a product of abnormal globin synthesis and composed of unused, precipitated globin chains. Characteristics: These are single or multiple, irregular, intracellular bodies refractile under reduced light. NOT seen on the Wright's stained smear but ONLY seen with supravital stains. G-6-PD deficiency - defect of HMP causes Heinz body formation after exposure to oxidative agents Post-splenectomy Thalassemic syndromes with unbalanced globin chain synthesis - beta thalassemia major (excess alpha chains) and alpha thalassemia intermedia/hgb H disease (excess beta chains). 8. Malarial inclusions Characteristics: A variety of irregular bluish structures with small red chromatin granules of "malarial" pigment which is derived from the hemoglobin of the RBC. The inclusions may be ringed, segmented or massive forms depending on the maturity of the parasite. The ringed form must be differentiated from a platelet on a red cell. Spread by the mosquitoes of genus Anopheles. Associated with infestation of: Plasmodium vivax (Schuffner's granules) Plasmodium falciparum (Mauer's dots) Plasmodium malariae Plasmodium ovale

7 E. VARIATIONS IN RED BLOOD CELL PATTERN/DISTRIBUTION Red cells are normally distributed evenly on the blood smear Rouleaux - property of plasma, due to abnormal or increased proteins. Characteristics: Stacking or coining pattern of red blood cells on the blood smear. Blue background on smear microscopically and may look very blue macroscopically. Multiple Myeloma or Waldenstrom's macroglobulinemia Chronic inflammation (high fibrinogen) 2. Agglutination Characteristics: Clumping of RBC's with no pattern. May see visible agglutination when the blood smear is prepared (grainy appearance). Cold autoimmune hemolytic anemias - cold-reacting autoantibodies F. ARTIFACT A well-made, properly stained smear is essential to prevent erroneous morphologic evaluation of the RBCs. Often times, types of specific poik may form as artifact...this may be due to an improperly made smear or improper/excess anticoagulant may alter the cells. Precipitated stain or water artifact can mimic RBC inclusions. A pushed slide may result in the smashing of red cells in the area of the smear where the morphology is done (where the cells just touch). The red cells may appear to be spherocytes, target cells or ovalocytes. If you see a specific poikilocyte (e.g., spherocytes) evenly distributed among normal appearing cells and throughout the entire smear, then chances are these cells are genuine. If the abnormality is only present on the edge of the slide or not found throughout the smear, it is probably artifact. Red blood cells that are in improper anticoagulant or have been in the proper anticoagulant too long may appear to be crenated or as acanthocytes. If you question a smear of this type, look in another area of the smear, make a new smear or check the circumstances of collection. Note: Some of the study slides may have oil artifact (shiny!).