CBC & PCV Flashcards
What 3 veins is blood most commonly collected from? What gauges are commonly used?
- jugular vein
- cephalic vein
- saphenous vein - lateral in dogs, medial in cats
18-22 gauge needle in small animals to prevent hemolysis
In what kind of tube is blood collected into for a complete blood count (CBC)? Why?`
purple top tube with sodium or potassium EDTA that chelates calcium and other divalent cations to inhibit the coagulation cascade (anticoagulants)
results in the separation of plasma, which contains clotting factors
- serum is void of clotting factors
What 3 values do the automated hematology analyzers measure?
- WBC: total WBC count, neutrophils, eosinophils, basophils, monocytes, lymphocytes
- RBC: RBC count, hemoglobin, hematocrit, MCHC, MCH, MCV, reticulocyte count
- platelet counts
What do refractometry and heat precipitation measure?
plasma protein
fibrinogen
What is used to analyze hemoglobin concentration? How does this work?
spectrophotometry
blood sample is aspirated into the analyzer and a chemical agent is added to lyse cells, which liberates hemoglobin and absorbance of light at a specific wavelength is proportional to concentration of hemoglobin
What rule is used as an internal quality control check for hemoglobin concentration?
hemoglobin = 1/3 of hematocrit value
If hematocrit is 33% what should hemoglobin concentration be?
~11 g/dL
What 2 calculated values are gained from automated hematology analyzers?
- mean cell hemoglobin (MCH)
- mean cell hemoglobin concentration (MCHC)
How is mean cell hemoglobin concentration calculated? What information does it provide?
calculated from hemoglobin concentration and hematocrit
Hgb/PCV x 100
index for quantity of hemoglobin relative to volume of packed RBCs
What are the 2 common methodologies of cell counting and sizing used by automated hematology analyzers?
- electrical impedance (Coulter technology)
- flow cytometry
How does electrical impedance work? What results does it yield?
- each cell within the whole blood is bathed in an isotonic diluent and passed between 2 electrodes through an aperture
- cells interfere with electrical current as it passes through
- change in impedance is proportional to cell volume
cell count, measure of cell volume, and a 3-part WBC differential (granulocytes, lymphocytes, monocytes)
How does flow cytometry work? What are the 2 major results it yields?
- single cells within the whole blood pass through a laser beam
- physical properties of the cell scatter light to different degrees and at different angles relative to the light source
- degree of scatter in the direction of the laser beam = forward scatter (FSC) = cell size
- degree of scattering at different angles = side scatter (SSC) = internal complexity and granularity, 5-part WBC differential (neutrophils, eosinophils, basophils, lymphocytes, monocytes)
How is packed cell volume (PCV) measured?
portion of the EDTA whole blood is pulled into a microhematocrit tube, sealed, and centrifuged at high speed leaving 3 fractions:
- plasma (protein)
- buffy coat (WBCs, platelets)
- packed erythrocytes (RBC contents)
How is PCV read after centrifugation? How should it compare to hematocrit levels generated from the hematology analyzer?
spun microhematocrit tube is placed on a PCV card
should match closely, within 3%
How is plasma protein measured using PCV?
spun down hematocrit tube is broken between the plasma and buffy coat and the portion of plasma is placed on refractometer glass
How are blood smears performed?
- use a microhematocrit tube to apply a drop of blood at the frosted edge of the glass slide
- hold spreader slide at a 30 degree angle
- pull back spreader slide until the blood wicks across
- rapidly and lightly push the spreader slide to make a smear
What are the 3 components of a properly made blood smear? Where can cells be counted?
- feathered edge
- monolayer*
- body
How are blood smears typically dyed?
EOSIN - acidic dye that stains basic structures red (RBCs, eosinophil granules)
AZURE DYE - basic dye that stains acidic structures purple (nuclei)
