Platelet Counting Techniques Quiz

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Questions and Answers

What is the primary purpose of shaking the pipettes after dilution?

To ensure even temperature

To mix different types of cells

To prevent platelet clumping (correct)

To reduce viscosity of the solution

Why should the first five drops from each pipette be discarded?

To prevent contamination from previous samples (correct)

To achieve consistent drop size

To allow for better flow through the pipette

To ensure accurate volume measurement

What should be placed beneath the hemocytometer to prevent evaporation?

Dry paper towels

A layer of paraffin

Plastic wrap

Wet gauze or cotton pads (correct)

What is the function of the tally counter or cell counter in this procedure?

To count cells during the counting process Signup and view all the answers

How should the pipettes be used when charging the hemocytometer?

Using separate pipettes for each side Signup and view all the answers

For how long should the hemocytometer be kept covered before counting?

10 to 15 minutes Signup and view all the answers

Which part of the hemocytometer should be charged with the sample?

Each side should charge a different pipette Signup and view all the answers

What should NOT be done to the tips of the pipettes before charging the counting chamber?

They should be blotted with absorbent material Signup and view all the answers

What is the primary purpose of using Rees-Ecker diluting fluid in the blood sample dilution process?

To make platelets readily visible under the microscope. Signup and view all the answers

Which action should be performed first before drawing blood into the RBC pipette?

Remove excess fluid from the pipette. Signup and view all the answers

What should be done if excess blood is drawn into the RBC pipette?

Adjust the blood level to the exact 0.5 mark with NSS. Signup and view all the answers

What is the correct dilution ratio to be made with the Rees-Ecker solution?

1:200 Signup and view all the answers

What equipment is essential for viewing the diluted blood sample?

Microscope with LPO and HPO Signup and view all the answers

Which component of the blood sample collection is crucial to prevent the platelets from adhering to the walls of the pipette?

Cleaning the stem of the pipette before blood draw Signup and view all the answers

How should the blood sample be collected for dilution?

By venipuncture into a tube containing EDTA. Signup and view all the answers

What is the purpose of adjusting the blood level in the RBC pipette?

To ensure an accurate dilution ratio. Signup and view all the answers

What area is covered when counting 5 RBC squares in the hemocytometer?

0.20 mm² Signup and view all the answers

How should the results from both sides of the hemocytometer be handled?

The results should be averaged between the two sides. Signup and view all the answers

What is the maximum acceptable percentage difference between platelet counts on each side of the hemocytometer?

10% Signup and view all the answers

Which of the following methods can be used to verify the accuracy of the manual platelet count?

Conducting a platelet estimate on a Wright-stained blood film. Signup and view all the answers

What is the appearance of platelets when viewed under high power magnification?

Small, roundish, unevenly shaped structures. Signup and view all the answers

How many RBC squares are counted when assessing the area of 1 mm²?

25 RBC squares Signup and view all the answers

What is a crucial step to take before counting platelets in the hemocytometer?

Carefully place the hemocytometer to avoid disturbing the platelets. Signup and view all the answers

Which of the following techniques is not included in the methods for direct platelet count?

Microwave hemolysis method. Signup and view all the answers

What is the dilution factor used in the computation of manual platelet counts?

200 Signup and view all the answers

What is the reference method for manual platelet counts?

Brencher-Cronkite Method Signup and view all the answers

What area and depth combination is used to calculate the volume of diluted blood counted?

1 mm² x 0.1 mm Signup and view all the answers

Which is the normal value range for platelets per microliter of blood?

150,000-400,000 Signup and view all the answers

Which staining method is used to visualize cellular elements of blood in the indirect method?

Wright’s or Wright’s-Giemsa Stain Signup and view all the answers

What must be done prior to examining the blood smear for platelet counts?

Stain the smear with Wright’s stain Signup and view all the answers

How many consecutive fields are typically examined for platelet counts?

10 OIO Signup and view all the answers

Which of the following is NOT a material or equipment needed for the Brencher-Cronkite method?

Incubator Signup and view all the answers

What condition is indicated by a below normal platelet count?

Pernicious anemia Signup and view all the answers

Which of the following is a common source of error in platelet counting?

Not adjusting the light correctly Signup and view all the answers

When examining a blood smear for platelet counting, what should be ensured to observe?

RBCs should barely be touching each other Signup and view all the answers

What is the anticoagulant of choice to prevent platelet clumping?

EDTA Signup and view all the answers

What is 'platelet satellitosis'?

Platelets adhering around neutrophils Signup and view all the answers

Which condition is associated with thrombocytosis?

Post-splenectomy Signup and view all the answers

What is a common artifact that can mimic platelets under a microscope?

Bacteria and debris Signup and view all the answers

At which magnification should the final platelet count be conducted?

1000x magnification Signup and view all the answers

Study Notes

Principle of Blood Sample Dilution

Blood sample is diluted using Rees-Ecker diluting fluid to enhance platelet visibility under a microscope.
Prior rinsing of the RBC pipette with Rees-Ecker fluid prevents platelet adherence to the pipette walls.
Blood is drawn to the 0.5 mark in an EDTA evacuated tube; if excess, adjust with normal saline (NSS).
Immediate dilution with Rees-Ecker solution is essential to prepare a 1:200 dilution using two pipettes.

Charging the Counting Chamber

Pre-mix the pipettes by shaking for at least 60 seconds to prevent platelet clumping.
Discard the first five drops for accurate volume charging of the hemocytometer.
Hemocytometer should rest for 10-15 minutes in a covered container with moist gauze to prevent evaporation and facilitate settling of platelets.

Counting Platelets

Utilize a microscope to count platelets in five RBC squares of the hemocytometer; average counts from both sides.
Platelets appear as small, roundish, uneven structures under high power magnification.
Ensure the difference between totals counted on each side is less than 10% for accuracy.

Direct Platelet Count Methods

Brecher-Cronkite, Tocantins/Rees-Ecker, Guy and Leake’s, Nygard’s, Walker and Sweeney’s, and Van Allen’s methods.
Unopette is another calibrated tool used for platelet counting.

Brecher-Cronkite Method

A reference technique for manual platelet counting, focusing on average platelet numbers per square millimeter and dilution factor (200).

Normal Platelet Count Values

Typical range: 150,000 - 400,000 platelets per microliter or 150 - 400 x 10^3 platelets/uL.

Indirect Method of Counting

Staining involves a well-made smear with Wright’s or Wright’s-Giemsa stain for platelet visualization.
Examine 10 consecutive fields of the smear for accurate platelet counts.

Interpretation of Results

Below Normal: Thrombocytopenia associated with conditions such as aplastic anemia, pernicious anemia, acute leukemia, and idiopathic thrombocytopenia purpura.
Above Normal: Thrombocytosis linked to disorders like polycythemia vera and chronic myeloproliferative disorders.

Sources of Error in Platelet Counting

Light adjustment is crucial—imperfections can fade platelet visibility.
Miscounting due to bacteria or debris mimicking platelets.
Platelet clumping may require recollection of the specimen; use EDTA to prevent clumping.
General hemacytometer errors, such as overloading or miscounting borders, affect results.
Platelet satellitosis may occur with EDTA, causing platelets to surround neutrophils, resulting in an altered appearance.

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Description

Test your knowledge on the principles of blood sample dilution, charging the counting chamber, and counting platelets using a hemocytometer. This quiz covers essential techniques to enhance platelet visibility and prevent clumping during counting procedures.