Packed Cell Volumes Total Proteins and Blood Films Laboratory Procedures

PCV (Packed Cell Volume) In a CBC, we determine the number of RBC’s in several different ways. The quickest and easiest is called the microhematocrit/hematocrit, also referred to as the packed cell volume (PCV) The PCV will tell you if the animal is anemic or dehydrated.

Normal PCV Values Canine: 37 – 55% Feline: 30 – 45% Equine: 32 – 52% Bovine: 24 – 46%

Whole blood is collected in an anticoagulant (usually EDTA) and placed in a capillary tube. Microhematocrit tubes should be filled to the designated line, with one end plugged with clay sealant.

Blood sample should be spun in a microhematocrit centrifuge for 2-5 minutes Lay the tube in the centrifuge with the plugged end facing the outside of the centrifuge. Make sure that a balancing tube is placed opposite or have another sample across from yours. Cells are heavier than plasma and are compacted at the end of the tube that has the clay plug.

Reading your PCV

Plasma Evaluation Plasma color and transparency may be helpful in determining a diagnosis and should be recorded in your findings. Normal plasma is clear or a pale straw-yellow color Cloudy Serum = lipemic Reddish tinge = hemolyzed Yellow = icteric (indicates possible liver disease)

Concentration of total protein / total solids Plasma protein concentrations estimated by refractometry is an important component of the CBC in all species. Plasma used to determine the TP/TS is collected by breaking the hematocrit tube just above the buffy coat/plasma interface.

The plasma is allowed to flow onto the refractometer. (Blow gently through the open end of the hematocrit tube with the broken end of the tube over the prism of your refractometer.) Hold the refractometer up to the light and record your findings. Make sure to wipe your refractometer after each use!

Blood Films The blood film is used to perform the differential WBC count; estimate platelet numbers; and evaluate the morphological features of WBCs, RBCs and platelets. Wedge smears are prepared by placing a small drop of blood on a clean glass microscope slide

Blood films

Staining a slide Always stain using the lightest to darkest stain. Remember which side of your slide is up (clothes pins are marked “top”) Rinse off from back side of slide May heat fix to speed up process.

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 %)