Complete Blood Count
and Anemia
Clinical Pathology
Blood Composition
• Separates into three components:
• Red Blood Cells (RBC’s)
• White Blood Cells and platelets (buffy
coat)
• Plasma
• Bottom 1/3 to ½ of tube contains the
heaviest of cellular material (the RBC’s).
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.
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
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.
More Manual Procedures
• Absolute WBC: Total number
of white blood cells in the
blood.
• Unopette hematocytometer
test kits are used to lyses
RBC’s and to make a 1:100
dilution.
• WBC’s are counted within
the grid and calculated to
reflect the WBC in the
blood.
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.
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.
Red Blood Cell Indices
• PCV (hematocrit)
• Hemoglobin Concentration
• Total red blood cell count
• These are used to classify the type of
anemia.
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.
Clinical Signs of Anemia
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Pale mucous membranes
Exercise intolerance
Tachycardia
Panting
Icterus if anemia is caused by RBC
breakdown in bloodstream.
Classification of Anemia
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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
• RBC’s have decreased density of the characteristic hemoglobin color.
• Frequently observed in iron deficiency caused by chronic blood loss or
parasitism.
• Normochromatic
MCV
• Describes cells as normocytic, microcytic,
or macrocytic. Calculates the average
volume of rbc’s.
• 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
MCV causes of Increases
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Reticulocytosis
Congenital issues (poodles)
Cats with FeLv
RBC agglutination
B12 deficiency (rare)
MCV causes of decreases
• Abnormal Hgb synthesis (iron deficiency
from chronic blood loss is the most
common).
• Immature animals
• Dogs with PSS.
• Congenital (Akitas)
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%
MCHC causes if high
• Intravascular hemolysis
• Inaccurate Hgb reading (Heinz bodies,
lipemia, etc).
• Machine error
• True hyperchromasia does not exist.
MCHC causes if low
• Small reticulocytes
• Iron deficiency.
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
Wright’s stain, reticulocytosis with
methylene blue stain, may also see
increased numbers of nucleated RBC’s
• Nonregenerative anemia:
• Indicates anemia is result of bone
marrow defect.
• No response evident in peripheral
blood.
• Marrow examination may be helpful
with the diagnosis.
Reticulocyte Count
• Probably the most important diagnostic tool
used in the evaluation of anemia.
• Expressed as a % of the RBC’s present.
• Corrected to take in account the reduced
number of circulating RBC’s 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
RBC’s daily so the reticulocyte count should
be 0.5-1.5%.
Reticulocyte count continued
• Expressed as # of retics/100 RBC’s
• Some species variation in reticulocyte
response exists.
• Normal horse and cattle blood do not
have reticulocytes.
• CRC= (patient Hct)/(Normal Hct) x
reticulocyte count
Example
•
Dog with an observed reticulocyte count of 9 % and Hct of 25%. Normal
Hct is 45.
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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
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.
Chronic Blood Loss
• Blood is lost slowly and continuously for a period of time.
• Body compensates for anemia by lowering oxygenhemoglobin 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
RBC’s 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.
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
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: RBC’s are lysed
following phagocytosis.
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