Platelet counts can be made by visual counting or electronic counters. Phase contrast microscopy helps considerably in recognising and counting platelets. After 2 minutes an improved Neubauer's chamber is charged and placed under a petridish with moist filter paper for 20 minutes. This allows the platelet to settle on the surface of the counting chamber. The moist filter paper keeps the air moist and prevents drying of the chamber.
Platelets appear as highly refractile particles under the high power lens.
Platelets are counted in one or more square mm. Atleast 100 platelets must be counted. With a drop, a thin smear is prepared and stained with Leishman's or Wrights stain. With another drop of blood, the RBC count is done simultaneously. On the smear 1000 RBCs are counted and the number of platelets seen whilst counting is noted.