Platelet Function. Platelet must be adequate in number and function to participate optimally in homeostasis. The functions of platelets in homeostasis include; Maintenance of vascular integrity Initial arrest of bleeding by platelet plug formation
The functions of platelets in homeostasis include;
Platelets adhering to damaged endothelium and undergoing activation
Aggregation of platelets into a thrombus
in flowing blood
Platelets adhering to subendothelial space
Adapted from: Ferguson JJ. The Physiology of Normal Platelet Function. In: Ferguson JJ, Chronos N, Harrington RA (Eds). Antiplatelet Therapy in Clinical Practice. London: MartinDunitz; 2000: pp.15–35.
FIRM, BUT REVERSIBLE
Scanning electron micrograph of discoid, dormant platelets
Activated, aggregating platelets illustrating fibrin strands
Adapted from: Kuwahara M et al. Arterioscler Thromb Vasc Biol 2002; 22: 329–34.
Substances that can induce platelet aggregation include;
1- A clean venipuncture is crucial. Hemolyzed samples should not be studied because RBCs contained ADP.
2- Plasma from fasting patients is preferred for testing. Lipemic samples may obscure change in optical density owing to platelet aggregation.
3- Sodium citrate is the anticoagulant used in aggregation studies. In vitro aggregation is dependent on the presence of calcium ions.
4- Fibrinogen must be present in the test sample for aggregation to occur.
5- Aggregation studies should be performed at 37°C at a pH of 6.5 to 8.5. To help maintain platelet values, all samples, once collected, should be capped to prevent Co2 loss.
6- Test samples, should be maintained at room temp during processing. Cooling inhibits the platelet aggregation response.
7- Stirring is necessary to bring the platelets in close contact with one another to allow aggregation to occur.
8- It is essential that the patient refrain from taking any anti-inflammatory drugs, one week before the test. The drugs inhibit the platelet’s release reaction.
9- Aggregating reagents should be prepared fresh daily and brought to room temp before use. They must have known potency and be added in small volume.