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