What are platelets?
Platelets (thrombocytes) are cells in the blood that clump together to begin the clotting process. They are usually one of the first responders when there is injury and help initiate the inflammatory response of the innate immune system.
The four main platelet functions are:
- adherence to each other
- taking part synergistically with other coagulation factors
As necessary as platelets are, also necessary is their proper functioning, neither under-active nor hyperactive:
- Decreased platelet activation impairs clotting and results in bleeding.
- Increased platelet activation results in their aggregating together to obstruct blood flow in veins risking pulmonary emboli, or in arteries risking ischemia to tissues beyond the clot.
There are conditions when decreasing platelet function is desirable and for which antiplatelet medication is indicated:
- Acute coronary syndrome
- Myocardial infarction
- Secondary prevention of stroke
- Coronary artery stenting
- Deep vein thrombosis
- Congenital platelet disorders that cause arterial and venous thromboembolic events
- Non-steroidal Anti-inflammatory Drugs (NSAIDs)
- P2Y12 receptor antagonists, which block the platelet activation receptor
- Nitrates, which reduce platelet aggregation and adhesion
- Calcium channel blockers, which reduce platelet aggreagaion and adhesion
- Heparin, which reduces platelet adhesion
Other anticoagulants work other than by affecting platelets directly. An example is warfarin, which interferes with vitamin K, important in clotting.