Flashcards in Haematology - PCV Deck (18)
What should blood be for haematology testing?
Fresh (no more than 24hrs old, one hour for blood smears ).
EDTA anticoagulated (Heparin is used for some exotics species).
What are the two parts of a haematology assessment?
Numerical results (quantitative)
Cell morphology (qualitative)
Describe quantitative assessment
This looks at the quantity of a range blood parameters and is commonly carried out using a wide range of commercial analysers. Some of the basic tests can/ should also be performed manually.
Define a HCT/PCV quantitiative assessment
This is a measurement of the portion of blood that is made up of red blood cells and is expressed as a percentage.
What does a high PCV indicate?
A high percentage indicates that there are a high number of red blood cells within the sample and a low amount of plasma. This could potentially indicate dehydration or polycythaemia.
What might a ow percentage PCV indicate?
The lower the percentage the less red blood cells are contained within the sample and the more plasma. This could potentially indicate anaemia or aggressive fluid therapy administration.
What equipment is needed for a quantitative assessment?
Fresh blood sample (EDTA)
Plain capillary tube
Hawksley reader or equivalent
What is the role of a centrifuge during PCV assessments?
Centrifugation of the prepared sample separates the blood into its component parts.
Describe the appearance and what this means once a PCV has been centrifuged
The top, straw coloured, layer consists of plasma containing water, proteins, glucose, clotting factors and electrolytes.
WBC’s form the middle layer known as the ‘buffy coat’.
RBC’s, which are the heaviest particles fall to bottom of the haematocrit tube.
How do you calculate the PCV percentage?
Automated haematology analysers will perform a haematocrit, however the manual PCV is deemed most accurate.
To ensure accuracy it is considered ‘best practice’ to obtain a mean result from at least 4 sample.
A number of PCV readers are available for use:
The ‘Hawksley’ reader is the most common
The stat spin microhaematocrit reader.
What are the average reference ranges for PCV in dogs and cats?
Dogs = 37-55%
Cats = 24-45%
What does each 1% PCV increase indicate?
10ml/kg fluid loss has occurred and should be added on to the fluid therapy deficit calculation.
Why are greyhounds considered differently when carrying out a PCV assessment?
Certain Sighthound breeds of dog e.g. greyhounds can have a healthy high-normal PCV, HCT, RBC, MCV, MCHC.
This is considered partly due to selective breeding for athleticism and high oxygen carrying capacity for superior track performance.
What is total protein?
Total protein (also referred to as total solids) is the amount of albumin and globulin contained within the plasma/serum.
This test gives an approximation of this value as plasma will also contain non-protein solids - glucose, cholesterol, clotting factors, urea etc.
It provides a quick guide to the mechanisms for an increase or decrease in PCV readings.
More accurate total protein readings should be obtained from a chemistry analyser or panel.
What equipment is needed to carry out a TP assessment?
A recently centrifuge microhaematocrit tube.
A refractometer (as used for urinary specific gravity)
How do you calibrate the refractometer?
To ensure accuracy of results it is important to calibrate the refractometer using distilled water.
Place 1-2 drops of distilled water on to the reading plate.
Hold the unit up to a good light source and look through the eye piece.
The blue section should begin at the 1.000 line on the urine Sg scale on the right hand side. This scale is used for calibration ONLY for a TP reading.
Describe the required technique for TP assessment
Wearing gloves, take the spun haematocrit tube between tube and for finger on both hands. Carefully Snap the tube (just above the buffy coat layer) to separate out the RBC and plasma portions of the sample
A set of nail clippers can be used to cut the tube if it is difficult to break
Holding the tube between thumb and forefinger place 2-3 drops of plasma onto the reading plate.
Hold the unit up to your eye and read and record the TP using the ‘serum P’ scale on the left hand side.
Record your findings using the units g/dl (grams per decilitre)