Here we will talk about the method only and we don’t mention the condition in which the PLTs increased or decreased but we will mention it in anther posts
The aim and the Value of test:
A platelet count may be requested to investigate abnormal skin and mucosal bleeding which can occur when the platelet count is very low . Platelet counts are also performed when patients are being treated with cytotoxic drugs or other drugs which may cause thrombocytopenia.
Principle of the test
Blood is diluted 1 in 20 in a filtered solution of ammonium oxalate reagent which lyzes the red cells. Platelets are counted microscopically using an Improved Neubauer ruled counting chamber and the number of platelets per litre of blood calculated.
Use EDTA anticoagulated venous blood.
Capillary blood should not be used because plateletsclumpas the blood isbeing collected
1) Counting chamber (hemocytometer)
The counting chamber recommended for cell counts is
– A metallized surface (‘Bright-line’)
– Double cell Improved Neubauer ruled chamber.
Non-metallized haemocytometers: While these are less expensive, they are not recommended because the background rulings and cells are not as easily seen which makes it is more difficult to count PLTs reliably using this type of chamber . Non-metallized chambers are also more difficult to fill.
2) Counting chamber cover glasses
Special optically plane cover glasses of defined thickness (designed for use with hemocytometers) are required.
Other cover glasses must not be used.
Manufacturers of counting chambers provide two cover glasses with each chamber.
The laboratory should always keep in stock spare cover glasses.
3) Pipettes/calibrated capillaries and safe filling device
We need 3 types of Pipettes
First: Graduated Pipette of 1 ml volume to get the volume needed from the diluting fluid
Second: Pasteur pipette of a capillary pipette to mix the blood sample and with diluting fluid
Third: Calibrated pipette of 20 µl (0.02 ml, 20 cmm) to aspirate 20 µl accurately
In case of Calibrated Pipette:
==> You may buy a Calibrated pipette of 20 µl (0.02 ml, 20 cmm) e.g. Sahli is required to measure blood samples.
==> Of It may be supplied with hemocytometers by some manufacturers and it is called a Bulb Pipette. and there is 2 Bulb pipettes supplied; one for Red blood cell count and one for WBCs count,>>>>>>
Bulb Pipettes should not be used for counting PLTs because it is not possible to obtain reliable mixing of the blood and diluting fluid inside the bulb of the pipette.
Bulb pipettes are also difficult to clean and expensive to replace
A safe pipette/capillary filler should be used to aspirate and dispense the blood. This can be a simple bulb filler or device. (CLIKC HERE TO SEE THE Pipette filter)
They are differ in the volume
You can use Variable Micropipette instead of all the THREE types
4) Hand counter
To count white cells accurately, a simple inexpensive mechanical hand tally counter or bead counter
Turning the knob on the side returns the counter to zero after each count.
CLICK HERE to see how you can prepared it manually in the lab
It is a diluting fluid contains Ammonium oxalate 10g/l
we use Ammonium Oxalate because it destroy PLTS making the platelet clear to count
See Procedure in Page 2