Complete Blood Count

Hematology

Hematology testing represents an important role of the veterinary technician: to provide accurate and reliable clinical laboratory test results to the veterinarian

A complete hematology profile is indicated for diagnostic evaluation of disease state, well animal screening, (e.g. geriatric) and screening tool before surgery

CBC Include

White and red blood cell countsHemoglobin concentrations Packed cell volume (PCV) Differential white blood film examination Calculation of absolute

values/erythrocyte indices

Types of Cellular Elements

Red blood cells – Erythrocytes White blood cells – Leukocytes Neutrophils Eosinophils Basophils Lymphocytes Monocytes Platelets – Thrombocytes (not true cells)

CBC

Total RBC count PCV Plasma protein concentration (TP) Total WBC Blood film examination: differential WBC

count, erythrocyte and leukocyte morphology, platelets estimation.

Reticulocyte count when the patient is anemic Hemoglobin concentration Erythrocyte indices

Quality control

Automated analyzers can provide accurate and cost-effective results. However, care should be taken in choosing the most appropriate instrument a clinic

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Cell counts

Counting of erythrocytes and leukocytes is a routine part of the CBC. Cells counts can be performed by manual and automated methods.

The total WBC (leukocyte) count is one of the most useful values determined in a CBC

Total RBC (erythrocyte) and platelet (thrombocyte) counts, although are more difficult and less accurate, may also be performed manually with a hemocytometer or by automated methods

Hemocytometer - Unopette

The “Unopette” system is a standardized method for enumerating leukocytes using fresh whole blood via a capillary puncture. This system is made up of the following components:

[1]    A reservoir that contains a premeasured volume (1.98mL) of a 3% glacial acetic acid solution.

[2] Self-filling, color coded 20 μL pipet. This pipet is constructed with one end that fits into the reservoir. This end is designated as the overflow chamber.

[3]    Pipet shield that covers and protects the pipet. The end of the “shield” is pointed for the purpose of puncturing the reservoir diaphragm before use.

[4]     See Figure 1 for an illustration of the Unopette system

The Hemacytometer has counting chambers used to determinate the number of cells per microliter (µl, sometimes referred to as cubic centimeters) of blood.

Several models are available, but the most common type used has two identical sets of fine grids of parallel and perpendicular etched lines called Neubauer rulings

Neubaur system

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Hematocrit - PCV

In the CBC, we determine the number of RBC’s in several different ways. The quickest and easiest is called the hematocrit, also referred to as the packed cell volume (PCV)

PCV / 6 = est RBC count / µL

Plasma Protein Concentration

Plasma Protein (TP) concentrations estimation by refractometry is an important component of the CBC in all species

The plasma used to determinate the PCV is collected by breaking the hematocrit tube just above the Buffy coat- plasma interface

Hemoglobin (Hgb)

Hemoglobin counts are usually done with an automated analyzer. The analyzer will mix a small amount blood with a solution to lyse the cells. It will then compare the color of the lysed cells to the normal

Hematology values

Erythrocyte Indices

Determination of erythrocyte indices is helpful in the classification of certain types of anemia

The erythrocyte indices include: the mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and MCH concentration mean corpuscular hemoglobin concentration (MCHC).

The indices can provide an objective measure of the size of the RBCs and their average hemoglobin concentartion.

Mean corpuscular volume (MCV) :

The MCV expresses the average volume (or size) of the individual erythrocyte. Using the total erythrocyte count, hemoglobin content and packed cell volume, it is possible to calculate the volume of an average erythrocyte and it’s hemoglobin concentration. Dividing the packed cell volume by the RBC concentration and multiplying by 10 determines the MCV.

Mean corpuscular hemoglobin concentration (MCHC)

The MCHC is the concentration of hemoglobin in the average erythrocyte, or the ratio of weight of hemoglobin to the volume in which it is contained.

The MCHC is calculated by dividing the hemoglobin concentration by the PCV (%) and multiplying by 100.

Mean corpuscular hemoglobin (MCH)

MCH is the weight of hemoglobin contained in the average erythrocyte. The MCH is calculated by dividing the hemoglobin concentration by the RBC concentration and multiplying by 10.

Blood films

Remember ! The blood film is used to perform the differential WBC count; estimate platelet numbers; and evaluate the morphological features of WBCs, RBCs and platelets.

Performing the Differential Cell Count

This is where the different white blood cells are tallied separately. This can be done by a blood counting machine, or by hand.

To manually count the different cells, first you must make a perfect slide. Stain the slide once it is dry.

Using a cell counter you will tally a total of 100 cells (this will make it easy to turn the numbers into a %)

The percentages will aid in initial diagnoses, interpretation should be based on the absolute numbers of the various cells.

Absolute numbers are obtained by multiplying the percentage by the total leukocyte count

Because 100 WBC are counted , the number of each WBC type observed is recorded as a percentage.

This is called the relative WBC countVarious counting devices are available to

help perform the differential WBCPage 44