Complete Blood Count and Anemia

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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 ½ of tube contains the heaviest of
  cellular material (the RBCs).

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HematocritPCV (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 1100 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