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

• Pale mucous membranes• Exercise intolerance• Tachycardia• Panting• Icterus if anemia is caused by RBC

breakdown in bloodstream.

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• 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

• 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.

• 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

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 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

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