The Bleeding Disorders Association of the Southern Tier
 (Member organization of the Hemophilia Federation of America)

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What are Platelet Disorders?

The hemostatic system consists of platelets, coagulation factors, and the endothelial cells lining the blood vessels. The platelets arise from the fragmentation of the cytoplasm of megakaryocytes in the bone marrow and circulate in blood as disc-shaped anucleate particles for 7-10 days.

Under normal circumstances, the resistance of the endothelial cell lining to interactions with platelets and coagulation factors prevents thrombosis. When endothelial continuity is disrupted and the underlying matrix is exposed, a coordinated series of events are set in motion to seal the defect (primary hemostasis).

Platelets play a primary role in this process, interacting with subendothelium-bound von Willebrand factor (vWf) via the membrane glycoprotein (GP) Ib complex. This initial interaction (platelet adhesion) sets the stage for other adhesive reactions that allow the platelets to interact with each other to form an aggregate

Platelet Disorders

Thrombocytopenia (THROM-bo-si-to-PE-ne-ah) is a condition in which your blood has a lower than normal number of blood cell fragments called platelets (PLATE-lets).

Platelets are made in your bone marrow along with other kinds of blood cells. They travel through your blood vessels and stick together (clot) to stop any bleeding that may happen if a blood vessel is damaged. Platelets also are called thrombocytes (THROM-bo-sites) because a clot also is called a thrombus.


When your blood has too few platelets, mild to serious bleeding can occur. This bleeding can happen inside the body (internal bleeding) or underneath or from the skin (external bleeding).

A normal platelet count is 150,000 to 450,000 platelets per microliter of blood. A count of less than 150,000 platelets per micro liter is lower than normal. But the risk for serious bleeding doesn't occur until the count becomes very low-less than 10,000 or 20,000 platelets per micro liter. Milder bleeding sometimes occurs when the count is less than 50,000 platelets per micro liter.

Many factors can cause a low platelet count, such as:

The body's bone marrow doesn't make enough platelets. The bone marrow makes enough platelets, but the body destroys them or uses them up.

The spleen holds on to too many platelets. The spleen is an organ that normally stores about one-third of the body's platelets. It also helps your body fight infection and remove unwanted cell material.

A combination of the above factors. How long thrombocytopenia lasts depends on its cause. It can range from days to years.

The treatment for this condition also depends on its cause and severity. Mild thrombocytopenia often doesn't require treatment. If the condition causes or puts you at risk for serious bleeding, you may need medicines or blood or platelet transfusions. Rarely, the spleen may need to be removed.


Thrombocytopenia can be fatal, especially if the bleeding is severe or occurs in the brain. However, the overall outlook for people who have the condition is good, especially if the cause of the low platelet count is found and treated.



Platelets contain two unique types of granules:

Alpha granules- The alpha granules contain hemostatic proteins such as fibrinogen, vWf, and growth factors (eg, platelet-derived growth factor).

Dense granules- The dense granules contain proaggregatory factors such as adenosine 5'-diphosphate (ADP), calcium, and 5-hydroxytryptamine (serotonin).

During activation, the granules are centralized and their contents are discharged into the lumen of the open canalicular system, from which they are then released to the exterior (the release reaction).

Once activated, platelets have two major mechanisms to recruit additional platelets to the growing hemostatic plug. They release proaggregatory materials (eg, ADP) by the release reaction, and they synthesize thromboxane A2 from arachidonic acid.

For more specific and factual information on Platelete Disorders, including cause, symptoms, diagnosis, treatments, and more visit: