complete blood count and anemia clinical pathology
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- Complete Blood Count and Anemia Clinical Pathology
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- Blood Composition Separates into three components: Red Blood Cells (RBCs) White Blood Cells and platelets (buffy coat) Plasma Bottom 1/3 to of tube contains the heaviest of cellular material (the RBCs).
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- Hematocrit=PCV (Packed Cell Volume) To determine hematocrit, whole blood is centrifuged to pellet the red blood cells. Plasma remains on the top of the red cells. The fraction of blood that is packed is the hematocrit and is read as a percentage.
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- Complete Blood Count Provides a minimum set of values and is cost effective. Can be done manually or with automated systems. CBC should contain: Packed Cell Volume (PCV or Hct) Plasma Protein Concentration Total White Blood Cell count Blood smear with morphology WBC differential count Reticulocyte count
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- Manual Procedures PCV- whole blood is collected in anticoagulant, placed in capillary tube, sealed, centrifuged and read. Total protein- plasma is read with a refractometer.
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- More Manual Procedures Absolute WBC: Total number of white blood cells in the blood. Unopette hematocytometer test kits are used to lyses RBCs and to make a 1:100 dilution. WBCs are counted within the grid and calculated to reflect the WBC in the blood.
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- Manual Procedures Continued Differential Leukocyte Count: a relative count is performed by counting and classifying at least 100 leukoctyes. This gives a percentage of each cell type which is then used to calculate the absolute numbers of each cell type. May use a counter in order to perform this count.
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- Instrumentation Electronic cell counters: based on the principle that cells are poor electrical conductors. Measured volume of diluted blood is drawn between two electrodes, causing a resistance in the electrical current. QBC: Quantitative Buffy Coat System Utilizes differential centrifugation and quantification of cellular elements in a specialized microhematocrit tube.
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- Red Blood Cell Indices PCV (hematocrit) Hemoglobin Concentration Total red blood cell count These are used to classify the type of anemia.
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- Anemia Literally means no blood but clinically means low total blood hemoglobin. Absolute anemia: most common, caused by failure to produce adequate numbers of cells or by a loss of cells at a rate greater than can be produced.
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- Clinical Signs of Anemia Pale mucous membranes Exercise intolerance Tachycardia Panting Icterus if anemia is caused by RBC breakdown in bloodstream.
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- Classification of Anemia By RBC size (MCV): Macrocytic Erythrocytes are larger than normal. Usually in the presence of regenerative anemia. May be seen in FeLv May see anisocytosis Normocytic Microcytic Cells are smaller than normal which has been determined by Mean Cell Volume (MCV). Usually occurs with iron deficiency caused by chronic blood loss or parasitism By Hemoglobin concentration (MCHC) Hypochromatic RBCs have decreased density of the characteristic hemoglobin color. Frequently observed in iron deficiency caused by chronic blood loss or parasitism. Normochromatic
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- MCV Describes cells as normocytic, microcytic, or macrocytic. Calculates the average volume of rbcs. MCV=(Hematocrit x 10)/RBC count in millions Ex: Canine patient with hematocrit of 42% and RBC count of 6 million/ul. Normal: 66-77
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- MCV causes of Increases Reticulocytosis Congenital issues (poodles) Cats with FeLv RBC agglutination B12 deficiency (rare)
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- MCV causes of decreases Abnormal Hgb synthesis (iron deficiency from chronic blood loss is the most common). Immature animals Dogs with PSS. Congenital (Akitas)
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- MCHC Mean Corpuscular Hemaglobin Concentration describes cells as normochromatic or hypochromatic. MCHC= (Hgb)/(Hct) x 100 Ex. Same patient as before with Hgb content of 14 g/dL Normal: 31-36%
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- MCHC causes if high Intravascular hemolysis Inaccurate Hgb reading (Heinz bodies, lipemia, etc). Machine error True hyperchromasia does not exist.
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- MCHC causes if low Small reticulocytes Iron deficiency.
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- Classification According to Bone Marrow Response Regenerative anemia: Characterized by evidence of increased production and delivery of new erythrocytes into circulation. Usually suggests an extra bone marrow cause (blood loss, hemolysis, etc.)., Diagnosis: Peripheral blood smear. Will see macrocytosis, polychromasia with Wrights stain, reticulocytosis with methylene blue stain, may also see increased numbers of nucleated RBCs
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- Nonregenerative anemia: Indicates anemia is result of bone marrow defect. No response evident in peripheral blood. Marrow examination may be helpful with the diagnosis.
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- Reticulocyte Count Probably the most important diagnostic tool used in the evaluation of anemia. Expressed as a % of the RBCs present. Corrected to take in account the reduced number of circulating RBCs in the anemic animal. Called CRC or Corrected Reticulocyte Count The lifespan of a normal RBC is about 100 days. Bone marrow should replace 1 % of the RBCs daily so the reticulocyte count should be 0.5-1.5%.
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- Reticulocyte count continued Expressed as # of retics/100 RBCs Some species variation in reticulocyte response exists. Normal horse and cattle blood do not have reticulocytes. CRC= (patient Hct)/(Normal Hct) x reticulocyte count
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- Example Dog with an observed reticulocyte count of 9 % and Hct of 25%. Normal Hct is 45. Interpretation A (expressed in %): Normal Less than or equal to 1 in dog Less than or equal to 0.4 in cat Mild Dog: 1-4 Cat: 0.5-2 Moderate Dog: 5-10 Cat: 2-3 Marked Dog: greater than 10 Cat: 3-4
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- Blood Loss Anemia Results from excessive hemorrhage although source can be subtle. Must determine if blood loss is internal or external. Possible causes: Trauma Persistent bleeding lesions Thrombocytopenia Coagulopathies Heavy parasitism Iatrogenic causes
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- Acute Blood Loss Anemia due to loss of blood in a sudden episode. All RBC parameters are normal for the first 12 hours. Hypovolemic shock can be apparent prior to a decreased PCV. Anemia will be normocytic, normochromatic, and apparently unresponsive with a low CRC. By day 4-5, the retic count increases and the anemia appears responsive.
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- Chronic Blood Loss Blood is lost slowly and continuously for a period of time. Body compensates for anemia by lowering oxygen- hemoglobin affinity, preferential shunting of blood to vital organs, increased cardiac output (tachycardia), and increased levels of erythropoietin. Anemia remains unresponsive unless iron stores are depleted. With decreasing iron stores, erythropoiesis is limited and RBCs become smaller and deficient in Hgb (microcytic and hypochromic). Clinical signs include lethargy, weakness, decrease exercise tolerance, anorexia, pallor, lack of grooming, mild systolic murmur.
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- Diagnostic Tests Hemogram: may see increased WBC and platelets. Total protein: decreased Coagulation testing: platelet count, PT, PTT, ACT. Fecal Float: Hookworms, Whipworms Fluids analysis from body cavities
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- Hemolytic Anemias Result of increased erythrocyte destruction within the body. Intravascular hemolysis: desctruction of erythrocyctes within the blood vessels and loss of Hgb from the cells. Extravascular hemolysis: RBCs are lysed following phagocytosis.
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- Differentials Immune-mediated disease: AIHA, drug induced, neonatal isoerythrolysis. Parasitic: Ehrlychiosis, Babesiosis, Hemobartonellosis, Anaplasmosis. Toxic: Heinz body anemias, snake venom, bacterial toxins. Infectious: EIA, Leptospirosis, Clostridia Fragmentation: Splenic torsion, Splenic neoplasia, DIC
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