In a platelet count, 50 µl EDTA blood (collected with an Eppendorf pipette) is
mixed in 950 µl dilution solution (collected with an Eppendorf pipette).
● This results in a dilution of 1:20.
● The mixture must stand approximately 5 minutes so that the erythrocytes are
completely lysed.
● Then the suspension is mixed and put into the counting chamber.
● The chamber is left in a moist environment for 20-30 minutes so the platelets can
settle without the chamber drying.
● Like the erythrocyte count, 80 small squares are counted.
● Calculation of the platelet count is achieved by using the formula below using
these factors:
- Number of platelets counted in the small squares.
- Dilution of the cell solution.
- Number of counted squares.
- Volume above a square.
- Conversion factor which is necessary in order to come to the volume of one
liter. Since we are moving in the µl area, this is equal to 106 (1 µl = 1 x 106 L or 1
L = 1 x 106 µl).
■ #Calculation:
Platelet counts / µl = Number of platelets counted × Dilution (20) ÷Number of
squares counted (80) ×volume of 1 small square (0.00025 µl)
i.e.
Platelet count / µl = (Number of Platelets counted × 20 ) ÷ (80 × 0.00025 µl)
i.e.
Platelet count / µl = (Number of Platelets counted × 20) ÷ (0.02 µl)
● Example with 200 counted platelets.
Platelet count / µl = (Number of platelets counted × 20) ÷ (.02 µl)
i.e. Platelets count / µl = (200 × 200) ÷ (.02 µl) = 200000 / µl