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Platelet Count Test Procedure

A blood platelet count is a blood test that measures the average number of platelets in the blood. Platelets help blood heal wounds and prevent excessive bleeding. High or low levels of platelets can be a sign of a serious condition.

Platelet Count test Procedure

Also Known As: Thrombocyte Count,  PLT,  Platelet Distribution Width,  PDW, Mean Platelet Volume,  MPV

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Test Panel: Hemoglobin, Red Blood Cells (RBC), HCT, MCV, MCH, MCHC, Platelets Count, White Blood Cells (WBC), DLC, ESR

There are two methods are explained

  • Manual Procedure
  • Automated Analyzer Procedure

Read More about Platelet Count:

Manual Procedure

Test Requirements

Reagent Prepration

Ammonium oxalate 10 g/l (1% w/v) diluting fluid. Important: Always filter the fluid before use

Test Procedure

Add 0.38ml (380ul)filtered ammonium oxalate diluting fluid in a test TubeAdd 20ul Blood Sample in Test Tubemix the diluted blood sample. Using a Micropipette held at an angle of about 45 , fill one of the grids of the chamber with the sample, taking care not to overfill the area.Leave the chamber undisturbed for 20 minutes.Dry the underside of the chamber and place it on the microscope stage. Using the 10 objective, focus the rulings of the grid and bring the central square of the chamber into view. Change to the 40 objective and focus the small platelets. They will be seen as small bright fragments.Count the platelets in the small squares marked “R” as shown in Figure

Report the number of platelets in 1 litre of blood. This is the actual number of platelets counted 10^9.
If 150 platelets are counted, the platelet count is 150 x 10^9/l.

Automated Analyzer Procedure

Most electronic blood cell analyzers including those manufactured by Beckman Coulter and Sysmex (Toa Medical), count blood cells by impedance.

Principle of impedance analyzers

Blood cells are diluted in a buffered electrolyte solution. A measured volume of the sample passes through an aperture tube (e.g. 100um in diameter) between two electrodes. Interruption of the current by the non-conducting blood cells alters the electrical charge and a pulse is produced. The amplitude of each pulse is proportioned to the volume of the cell which caused it. A threshold circuit ensures only those pulses that exceed the pre-set threshold level are counted. The cell count is determined from the total number of pulses obtained from a measured volume of blood.


Further information on electronic blood cell analyzers, their use, and sources of error can be study in the page of Equipments.

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Possible References Used

1 comment on Platelet Count Test Procedure

  1. This is very good write up, very explicit. Maybe I did not pay attention to that, reference range is not included. If it is , is the ranges to all the people groups. Also, the procedure for Ammonium oxalate preparation should be mentioned. Thank you

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