Types of platelet function disorders
- Hereditary platelet function disorders
- Disorders of platelet adhesion
- Disorders of platelet aggregation
- Disorders of platelet secretion
- Disorders of platelet procoagulant activity
- Combined abnormalities of number and function
- Acquired platelet function disorders
Hereditary platelet function disorders
Disorders of platelet adhesion
This rare disorder is called Bernard-Soulier Syndrome. It is caused by a deficiency on the surface of the platelet in an area called Glycoprotein Ib/IX. As a result, platelets fail to stick and clump together at the site of the injury. (See Figure 1, stage 3 in the Introduction section.)
The disorder is often first noticed during childhood. Children have frequent bruises, nose bleeds and bleeding in the mouth and gums. Some may experience gastrointestinal bleeding (bleeding in the gut).
Women may experience heavy menstrual bleeding, or their menstruations (periods) last longer than normal. This is called menorrhagia.
Blood tests show:
- a prolonged bleeding time (bleeding time is a measure of the time it takes for a simple cut to stop bleeding)
- a low platelet count (this means that there are fewer platelets than normal)
- that the platelets appear larger than normal when seen through a microscope
- that the platelets do not clump together in response to ristocetin.
Disorders of platelet aggregation
This rare disorder is called Glanzmann Thrombasthenia. It can be life-threatening. It is caused by a deficiency of a protein on the surface of the platelet, called Glycoprotein IIb/IIIa. As a result, platelets fail to form a plug at the site of an injury. (See Figure 1, stage 3 in the Introduction section.)
Like Bernard-Soulier Syndrome, children experience bruising, nose bleeds and bleeding in the mouth and gums.
Women may experience heavy or prolonged menstrual bleeding (menorrhagia) and bleeding at the time of childbirth.
Blood tests show:
- that bleeding time is much longer than normal
- that the platelets do not clump together at all (platelet aggregation is absent).
Disorders of platelet secretion
Three platelet function disorders involve platelet secretion.1) In Alpha Granule Deficiency, called Gray Platelet Syndrome, there is a lack of important proteins within the alpha granule inside the platelet. This problem slows down normal platelet adhesion, aggregation and repair of the blood vessel. (See Figure 1, stage 3.)
Bleeding time is usually long and the platelet count may be low. A test of platelet aggregation shows some abnormalities. Seen through a microscope, platelets show an absence of granules.
2) In Dense Granule Deficiency, called Delta Storage Pool Deficiency, there is a lack of storage granules for certain substances needed for normal platelet activation. Their absence slows down platelet activation and blood vessel constriction. (See Figure 1, stages 2 and 3.)
Bleeding time is sometimes longer than normal. A platelet aggregation test shows an abnormal pattern. Examination of the platelets using an electron microscope shows an absence of dense granules.
Some people with this disorder also have abnormalities in hair colour, difficulties with vision and are more prone to infection.
3) Abnormalities of the granule secretory mechanism occur when the normal granules fail to release their contents when platelets are activated. People with this disorder have platelet dysfunction like that of individuals who have been given drugs such as aspirin to stop their platelets from clumping together.
Disorders of platelet procoagulant activity
This very rare disorder is called Scott Syndrome. Platelets fail to promote activation of the blood clotting proteins which are necessary in the formation of the fibrin clot. (See Figure 1, stage 4.)
Bleeding time and platelet aggregation are normal but there are abnormalities of the platelet surface membrane. Specific tests are required to determine platelet procoagulant activity if this disorder is suspected.
Combined abnormalities of number and function
Some hereditary disorders of platelet production show low platelet counts and platelets of abnormal size. Many of these conditions are associated with other medical problems such as:
In some of these conditions, platelet function may also be abnormal. Nevertheless, bleeding problems, in most cases, appear to be related to low platelet numbers, and not the functional abnormalities.
Acquired platelet function disorders
Platelet function can be affected by common drugs. These are:
Other drugs can also affect platelet function. These include:
- some antibiotics
- heart drugs
- blood thinners
Platelet function returns to normal when these medications are stopped.
Certain medical conditions can cause abnormal platelet function. These include:
- chronic kidney disease
- heart bypass surgery
- some forms of leukemia.