![]() ![]() ![]() Agglutination refers to small groups or clumps of RBCs that result from the interaction between bound antibodies on the surface of RBCs.Īnisocytosis is a qualitative measure of variability in RBC size. Rouleaux also may form normally in feline blood and as an artifact due to slow drying of the blood smear. ![]() Rouleau occurs with decreased negative charges on the RBC membrane caused by increased concentrations of positively-charged proteins in plasma (i.e., fibrinogen, immunoglobins), usually in association with chronic inflammatory disease. RBC distribution abnormalities include rouleaux and agglutination. Abnormalities are graded as slight, moderate or marked (or 1+ to 4+). ![]() RBC morphology is assessed qualitatively on a well-made blood smear and includes RBC distribution, anisocytosis, poikilocytosis, polychromasia/hypochromasia, and inclusions or organisms. Some new hematology analyzers determine the percentage and number of hypochromic (and hyperchromic) cells of different sizes. Increased MCH or MCHC is an artifact secondary to Heinz bodies, lipemia, or hemoglobinemia. MCH and MCHC indicate hemoglobin concentration decreased values indicate hypochromasia. The RDW is a quantitative index of variability in RBC size, and is increased in regenerative anemia and iron deficiency anemia. Agglutination can falsely increase the MCV. If both macrocytes and microcytes are present, the MCV may be normal. The MCV may be increased (macrocytosis) or decreased (microcytosis). RBC indices are quantitative indicators of RBC morphology. Quantitative Evaluation of RBC Morphology Changes in the distribution of the phospholipids may have profound effects on red cell shape and other cell properties. Movement of free cholesterol between plasma and lipid bilayer is rapid and dynamic membrane phospholipid turnover with plasma is a passive process that occurs very slowly. Because mature RBCs cannot synthesize lipids, they rely on a continuous exchange of lipids between their membranes and plasma lipoproteins for homeostasis. Membrane enzymes depend on the integrity of phospholipids for normal function. Phospholipids are asymmetrically distributed within the bilayer, with hydrophobic long chain fatty acids oriented towards the inner core of the membrane. Cholesterol is in the free, unesterified form phospholipids are a mixture of lecithin (phosphatidylcholine), phosphatidylethanolamine, sphingomyelin, phosphatidylserine, and phosphatidylinositol. The lipid bilayer of the erythrocyte membrane is a permeability barrier composed of about equal amounts of cholesterol and phospholipids. The cytoskeleton delimits membrane deformability and confers the physical properties necessary for normal shape changes during circulation. The principal proteins-spectrin, actin, protein 4.1, and ankyrin-form a hexagonal lattice that underlies and attaches to the lipid bilayer via trans-membrane proteins (band 3 and glycophorins). The cytoskeleton helps determine and maintain the shape of red cells through the arrangement and interactions of cytoskeletal proteins. Most shape changes result from alteration of the red cell membrane. Red cell morphology may be altered by alterations in lipid, iron and oxidative metabolism, immune-mediated disease, mechanical fragmentation, and by electrolyte or metabolic abnormalities. During erythropoiesis and during the 2-5 months spent in circulation, RBCs are exposed to the biochemical milieu of plasma and are reliant on the availability of biochemical precursors needed for membrane and hemoglobin synthesis. Red cell shape is a result of both the environment of the cell and its metabolic status. In this presentation, I will discuss the pathophysiologic mechanisms of RBC morphologic alterations in dogs and cats (with an emphasis on shape changes) and their significance in the diagnosis of disease. RBC morphology may provide important diagnostic information regarding the underlying cause of anemia and systemic disease. Evaluation and interpretation of red blood cell (RBC) morphology is an important component of a complete blood count (CBC). ![]()
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