Platelets Count

What sample is needed for Platelets Count?

1. This can be done on EDTA blood.
   1. This is stable for 5 hours at 23 °C and 24 hours at 4 °C.
2. Take capillary blood and dilute directly; this sample is stable for 3 hours.
3. Fetal blood is collected from the umbilical area percutaneously.
4. The platelets can be assessed on the DLC slide as well.

What are the indications for platelet count?

1. To diagnose the cause of petechial bleeding in the skin.
2. To find the cause of spontaneous bleeding.
3. In women with heavy menses.
4. This is advised in a patient on chemotherapy.
5. This is advised in case of bone marrow failure.
6. Platelets count is of value in thrombocytopenia seen in:
   1. Uremia.
   2. Liver diseases.
   3. Malignancies.

How is the Formation of Platelets?

1. Platelets are the smallest form of formed elements of blood.
2. The megakaryocytes in the bone marrow form platelets. These are the detached portions of the megakaryocytes.
3. Platelets are the smallest of the formed elements of blood.
   1. Platelets measure 3.0 x 0.5 µm in diameter.
4. These are non-nucleated, small, round, or oval, flattened disk-shaped structures.

What are the functions of Platelets?

5. The glycoprotein of the platelet surface is important in the platelet reactions of:
   1. Adhesion.
   2. Aggregation.
   3. Leading to plug formation during hemostasis.
6. Glycoproteins are:
   1. Glycoprotein 1a.
   2. Glycoprotein 111a.
   3. Glycoprotein 1b.
   4. Glycoprotein 11b.
7. The binding site for 11b/111a is a receptor for fibrinogen, which is important in platelet aggregation.
8. The membrane phospholipids known as factor 3 are important in converting coagulation factor X to Xa and prothrombin (factor 11) to thrombin (factor 11a).
9. Platelet activity is needed for:
   1. Blood clotting.
   2. Vascular integrity.
   3. Vasoconstriction.
10. In hemostasis, the steps are:
    1. Platelet aggregation that occludes the breaks in the vessel wall.
    2. Initiates the clotting mechanism.

How are the platelets distributed in the body?

1. The lifespan of platelets is roughly 7.5 days.
2. Of platelets, two-thirds are in the blood, and one-third are in the spleen.

What are the contents of platelets?

1. The glycocalyx is the outer membrane.
2. α-Granules.
3. Lysosomes contain neutral proteases, bactericidal enzymes, and acid hydrolases.
4. Dense granules contain ADP, ATP, and Calcium.
5. β-thromboglobulin functions are:
   1. Inhibits heparin.
   2. It is chemotactic.
   3. Promotes smooth muscle growth for the repair of vessels.
6. Platelet factor 4, inhibits heparin.
7. Platelet-derived growth factor (PDGF)  functions are:
   1. It promotes smooth muscle growth.
   2. It takes part in atherosclerosis and lipid metabolism.
8. Thrombospondin functions are:
   1. It mediates cell-to-cell interaction.
   2. It promotes platelet-to-platelet interaction.
9. Fibrinogen leads to fibrin formation.
10. Von Willebrand factor (VWF) promotes platelet adhesion.
11. Factor V is a cofactor in fibrin formation.
12. Factor VIII is also a cofactor for fibrin formation.
13. Fibronectin  functions are:
    1. It is a cellular adhesion molecule.
    2. It promotes platelet spreading.
14. Plasminogen is the precursor to plasmin and has a function in fibrinolysis.
15. High molecular weight Kinogen has a role in activating the intrinsic pathway via contact.
16. α2-Antiplasmin inhibits plasmin.

How will the Platelets be activated?

1. This may be transient, reversible, or irreversible.
2. After activation, the changes are:
   1. Initially, there is a pseudopod formation.
   2. There is a contraction.
   3. Adhesion.
   4. Change in shape.
   5. There is a stickiness.
   6. There is aggregate formation.
   7. There is a platelet plug formation.
   8. There is the release of chemical secretions.
   9. The last step stabilizes the platelet plug by forming a fibrin mesh over the platelet aggregates.

What is the normal platelet count?

Source 1 

• To convert into SI unit x, 10⁶ = x 10⁹/L

Source 2 

1. Thrombocytopenia occurs when the count is less than 100,000 /cmm.
2. Thrombocytosis occurs when the count is more than 400,000 /cmm.
3. Thrombocythemia occurs when the count is above one million /cmm.

What are the Methods for counting platelets?

1. By automated hematology analyzers.
2. Direct smear also gives information about platelets’ size, shape, and clumping.
3. Direct count from the peripheral blood smears.
   1. Count platelets on an oil objective in 10 fields and multiply by 2000, which gives a rough idea of the count.
   2. Platelets in 10 field X 2000 = Total platelets.

What is the manual method of platelet count?

1. Take 20 µL of blood.
2. Add 1.8 mL of 1% ammonium oxalate.
   1. Ammonium oxalate will lyse the RBCs and WBCs, while Platelets will remain intact.
3. Leave for 15 minutes to complete the lysis of RBCs.
4. Mount the Neubauer chamber.
5. Leave the chamber for 15 minutes in high humidity.
6. Count the large central square labeled as P.

1. How will you calculate the platelets?
   1. Area of 5 squares in the central area = 0.2 sq. mm
   2. The depth of the chamber is 0.1 mm.
   3. The volume of 5 squares in the central area = 0.2 x 0.1 µL   =  0.02 µL
   4. Dilution of the blood sample = 1:20
   5. If P number of platelets is counted in 0.02 µL
   6. The number of platelets /µL = P x 20 x 1/0.2
   7.  = P x 20 x 50
   8. = P x 1000
   9. Note: You can use the constant factor of 1000.

What is another method of platelet counting?

1. Under 400x magnification while adjusting the light.
2. Count all 25 squares in the large central area.
   1. Duplicate the counting procedure.

3. Multiply the counted platelets by 1000 = Total platelet count/cmm.
   1. Multiply the above number of platelets by 10⁶ to get the count in SI units.
4. Example:
   1. Suppose the platelet count in 25 squares (Central square) = 300 x 1000 = 300,000/cmm
   2. To convert  into SI units = 300,000/cmm x 10⁶
   3.                                             = 300 x 10⁹/L

What are the sources of errors in platelet counting?

1. To minimize the error of counting platelets manually:
   1. Mix thoroughly, diluting fluid before filling the chamber.
   2. Avoid platelet clumping.
   3. Improper dilution.
   4. Not properly filling the chamber.
   5. Avoid microclot formation.
   6. Keep in mind the calculation errors.
   7. Contaminated counting fluid.
   8. In case of clumping of the platelets.
   9. Run the test in duplicate and then get the average of the two results.
   10. If taking blood from the finger, then don’t squeeze the finger.
   11. The count is lower on the skin puncture sample than on the venous blood sample.

What is the mechanism of thrombocytopenia?

1. This may be due to decreased production of bone marrow. This may be due to the following:
   1. Bone marrow failure.
   2. Infiltration of the bone marrow by tumors or fibrosis.
2. Destruction or sequestration of the platelets by hypersplenism.
3. Antibodies destroy the platelets.
4. Destruction of the platelets by infection or drugs.
5. Increased utilization of disseminated intravascular coagulation.
6. In severe hemorrhage, which leads to loss of platelets.
7. A large blood transfusion leads to a dilutional effect.

What are the causes of thrombocytopenia?

1. Idiopathic Thrombocytopenia ITP.
2. Hypersplenism.
3. Anemias are pernicious, aplastic, and hemolytic.
4. After a massive blood transfusion
5. An infection, such as viral or bacterial,
6. Chemotherapy treatment.
7. HIV infection.
8. Leukemias, carcinoma, and myelofibrosis. This is due to the infiltration of the bone marrow.
9. D I C.
10. Toxemia of pregnancy, eclampsia.
11. Antiplatelet antibody.
12. Renal failure.
13. Inherited diseases like Wiskott-Aldrich syndrome.
14. An autoimmune disease like systemic lupus erythematosus

What are the causes of Thrombocytosis?

1. Malignant tumors like leukemia and lymphoma,
2. Polycythemia vera.
3. Splenectomy.
4. Iron deficiency anemia.
5. Autoimmune diseases like Rheumatoid arthritis and SLE.
6. Hodgkin’s lymphoma
7. Chronic pancreatitis and inflammatory bowel disease.
8. Tuberculosis.

What is the Critical value of platelets?

• The patient may develop spontaneous bleeding when the platelet count is < 20,000 /cmm.
• Platelet counts > 50,000 /cmm usually show no bleeding.

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