Anti-platelets

Question 1

What size are platelets and where do they originate?

Answer 1

Platelets are tiny discs, 2-4 μm in diameter, formed by the gradual fragmentation of megakaryocytes in the bone marrow.

This process is controlled by thrombopoietin (TPO), a protein produced by the liver and kidneys at an almost constant rate, although the rate is increased in inflammatory states.

Question 2

What is the platelet life span?

Answer 2

8-12 days before being removed by tissue macrophages, especially in the spleen.

Question 3

What are the three mediators of platelet activation?

Answer 3

1. thromboxane A2 (TxA2) is formed from arachidonic acid by a pathway that starts with cyclooxygenase-1 (COX-1). TxA2 is a potent vasoconstrictor and also binds to receptors on platelet membranes, accelerating activation.
2. adenosine diphosphate (ADP)
3. thrombin

Question 4

What are the three mediators of platelet activation?

Answer 4

1. thromboxane A2 (TxA2) is formed from arachidonic acid by a pathway that starts with cyclooxygenase-1 (COX-1). TxA2 is a potent vasoconstrictor and also binds to receptors on platelet membranes, accelerating activation.
2. adenosine diphosphate (ADP)
3. thrombin

Question 5

What is the gold standard for testing platelet function?

Answer 5

LTA is the gold standard in the laboratory.

The platelets absorb light and therefore block transmittance through the test chamber. As the platelets aggregate, less light is absorbed so light transmittance increases. This change in light transmittance is plotted against time.

Question 6

How does Thromboelastoplasty work? (TEG)

Answer 6

In thromboelastography (TEG), blood is added to a plastic cup that is coated with something, often kaolin, that initiates clotting. A plastic ‘pin’ is placed over a torsion wire and lowered into the blood. The pin is rotated back and forth through a small angle and, as the blood clots, strands of fibrin create tension on the wire. The instrument plots this tension against time, producing a curve.