RBC indices Flashcards
Complete blood count is good for
Gives us a minimum set of values that are reliable and cost effective
Tests included in a CBC can be done with automated machines are manually
Complete blood counts includes
Total red blood cell count
Packed cell volume (PCV) or hematocrit
Plasma protein concentration (aka total protein-TP)
Total WBC count
Hemoglobin (Hb/Hgb) concentration
Erythrocyte indices
Blood film evaluation: differential count, morphology of WBC and RBC, platelet examination
These tests make up a hemogram
The total WBC count and differential count make up the leukogram
Packed cell volume (PCV) is what
Is is the percentage of whole blood made up of erythrocytes (RBCs)
This test can be used to evaluate the hydration status of the patient
It is also used to diagnose anemia or erythrocytosis
PCV is run as and is how accurate
This test can be run as a single test or as part of a CBC
This test is extremely accurate with an inherent error of ± 1%
How is PCV expressed
Hematocrit (Hct) or microhematocrit (mHct) is the PCV expressed as a volume
Ex. PCV= 42%, Hct= 0.42L/L
Sources of error in the PCV test
Failure to mix the blood sample properly
Hemolysis of the sample
Insufficient centrifugation time and/or speed which leads to incomplete packing of cells
Procedure for running a PCV*
Mix the blood gently- by gentle inversion of using a figure 8 motion
Fill two microhematocrit tubes about 75% full using capillary action
Hold tube horizontally until it is placed into the sealant, one end is inserted into the sealenat at least twice
Load the centrifuge by balancing the tubes, make sure the sealant end is towards the outer edge of the centrifuge
Follow the centrifuge instructions→ usually 2-5 minutes on the hematocrit setting
Turn the centrifuge on after securing the lid
Set timer (hematocrit setting)
Follow directions for the centrifuge
When the centrifuge stops, open it and examine the tubes
Once the sample has finished spinning, you can read the tubes
Requires two microhematocrit tubes to balance the centrifuge for quality control
Red ring on top will have heparin inside
Blue ring on top will not
How to read a PCV
Be sure to evaluate all three layers
The plasma layer- color and clarity
The buffy coat- width and color
The PCV- width
Yellow plasma in a PCV can indicate
Should be noted on the file, may be due to several problems
Liver disease
Hemolytic disorders
Nutrition supplements
Dehydration
Normal in plant and grain eaters (ruminants and poultry)
Due to carotenoids in the feed
Pink plasma in a PCV may indicate
Evidence of hemolysis
Usually due to poor collection or handling methods
May be due to intravascular disorders
Will affect other test results
White plasma can indicate
Lipedemia is due to the presence of fat in blood
Seen after eating
Rarely pathologic
Interdeers with many chemical tests
The middle layer in the PCV tube contains
(buffy coat)- contains the WBC & platelets, white appearance
It will appear red when there are significant numbers of nucleated RBCs present
The buffy coat
A normal buffy coat should be about the thickness of a dime (~1mm)
How do you read PCV
PCV is measured at the intersection of the top of the RBC mass and the buffy coat
Measured on a reader card
Results are in % and then converted to 0.XX L/L (always 2 decimal places)
Ex. PCV of 42%= Hct of 0.42L/L
Significance of PCV results
Used as a screening test for pathological conditions
Lower than normal values indicate anaemia
Can be falsely decreased if not enough blood was added to the blood tube
Diluted by anticoagulant
Higher than normal values indicate polycythemia or dehydration
Dehydration is more common
Make sure to mix you sample well immediately before filling the microhematocrit tubes
Normal PCV of canine
37-55%
Normal PCV of feline
30-45%
Normal PCV of equine
32-57%
Normal PCV of bovine
24-42%
Normal PCV of ovine
25-45%
Normal PCV of coprine
21-38%
Normal PCV of porcine
32-43%
Plasma protein concentration tests for
This test will give an estimate of the total protein concentration of the two sample
It requies a refracometer and two spun michrohemtocit tunes
How to perform a plasma protein concentration
After the PCV has been read, the tubes are carefully broken just above the buffy coat (within the plasma layer)
A few drops of plasma are placed on the prism of the refractometer
Let the plasma flow onto the refractometer, do not tap the tube on the crystal of the refractometer
Close the lid gently and look at the TP scale (it will be in g/100ml, an older refractometer it may be labelled as g/dL)
You will be reading the number on the scale at the light dark interface
Read on a refractometer
Normal values for most species
50-80 g/L
Lipedemia and hemolysis will falsely elevate the results
g/dL=g/100mL
Must be converted to g/L with no decimal places
9 g/100 mL → 1000mL = 1L
9g/100ml X 1000mL/1L = 90g/L
9g/dL → 10dl= 1L
9g/1dL x 10dL/1L= 90g/L
