Bleeding disorders may arise from problems with platelets, either from a low count in the blood or from dysfunctional platelets. A CBC, which includes a platelet count, may reveal a low number while platelet function tests may indicate that dysfunctional platelets are present. Several follow-up tests may be required to determine the cause.
Platelet deficiency (thrombocytopenia)
A number of conditions and factors can cause a low platelet count, also called thrombocytopenia. The causes typically fall into one of two general categories:
- Disorders in which the bone marrow cannot produce enough platelets
- Conditions in which platelets are used up (consumed) or destroyed faster than normal
Examples of conditions that can cause a low platelet count include:
- Idiopathic (immune) thrombocytopenia, also called idiopathic thrombocytopenic purpura (ITP), is caused by an autoantibody produced against platelets. It is one of the most common causes of low platelets. Acute ITP occurs more often in youth, is usually short-term, and typically follows a viral infection. This condition may resolve without treatment. Chronic ITP develops more slowly, typically lasts longer than 6 months, and occurs more often in adults. Because of the duration of the disease, this form may require treatment.
- Heparin-induced thrombocytopenia (HIT) results in low platelets when a person who is on or received heparin therapy develops an antibody. However, HIT is often associated with clotting, rather than bleeding. (For more on this, see the article on HIT Antibody).
- Thrombotic thrombocytopenia purpura (TTP) is an acute, potentially life-threatening though rare condition. It causes both clotting and bleeding. Tiny clots form and deposit in small blood vessels throughout the body. This clotting uses up platelets at an accelerated rate, leading to a low number of platelets and increased risk of bleeding.
- Certain drugs such as acetaminophen, quinine, sulfa antibiotics, digoxin, vancomycin, valium, nitroglycerine and gold salts are just a few examples that have been associated with a decrease in the number of platelets.
- Sepsis, especially that caused by a serious bacterial infection with Gram-negative bacteria
- Autoimmune disorders, such as lupus, where the body's immune system produces antibodies that attack its own organs or tissues, causing increased destruction of platelets
- Cancer such as leukemia, lymphoma or another type that has spread to the bone marrow may affect the production of platelets by the bone marrow. As the number of cancer cells increases in the bone marrow, normal bone marrow cells are crowded out, resulting in fewer platelet-producing cells.
- Viral infections such as mononucleosis, hepatitis, HIV or measles
- Aplastic anemia – with this condition, the production of all blood cells is significantly affected.
- Massive blood (red blood cells) transfusion without giving platelets (thrombocytopenia due to dilution effect)
- Long-term bleeding problems (e.g., chronic bleeding from stomach ulcers)
- Chemotherapy or radiation therapy, which may affect the bone marrow
- Platelet consumption may be observed in various diseases and conditions. For example, disseminated intravascular coagulation (DIC) and hemolytic uremic syndrome (HUS) can result in fewer circulating platelets in the blood.
- Increased pooling (sequestration) of platelets in enlarged spleen (e.g., related to cirrhosis, myeloproliferative neoplasms)
The conditions and factors resulting in platelet dysfunction are either inherited or the result of some other disease or condition (acquired).
Examples of inherited platelet function disorders include:
- Glanzmann's thrombasthenia – affects platelets' ability to clump (aggregate)
- Bernard-Soulier syndrome – characterized by reduced platelet adhesion
- Storage pool disease – can affect platelet ability to release substances that promote aggregation
Acquired platelet dysfunction – those that are not inherited – may be due to chronic conditions or factors such as: