Blood platelets are fragments of cells. They are used by the body to help control bleeding. Low blood platelets is a condition called thrombocytopenia. When the platelets are low, bleeding takes longer to stop. When they are very low, spontaneous bleeds occur. Consequences may include blood loss through the GI tract, or strokes from bleeding in the brain. Diseases causing low platelets are divided into three categories. These include low production, breakdown outside the blood vessels and breakdown inside the blood vessels.
Low Production
Platelets are made in the bone marrow. Conditions affecting the bone marrow can result in decreased platelet levels. Cancers, such as leukemias and lymphomas can grow throughout the bone marrow, limiting the development of platelets according to "Harrison's Principles of Internal Medicine" by Anthony Fauci M.D. Infections such as HIV can also suppress bone marrow production of platelets. Drugs and toxins can do the same, such as chemotherapy agents.
Extravascular Breakdown
In addition to insufficient production, platelets may be produced and then broken down. If they are broken down outside the blood vessels, this is called extravascular thrombocytopenia. It most often occurs from liver and spleen diseases, which cause platelets to be trapped in the spleen. Examples include liver cirrhosis, which can cause blood to back up into the spleen, resulting in trapped platelets which are destroyed, according to "Robbins and Cotran Pathologic Basis of Disease" by Dr. Vinay Kumar. The spleen can also be enlarged by infections, such as mononucleosis, also known as mono or the kissing disease.
Intravascular Breakdown
Intravascular breakdown of platelets refers to their destruction in the blood vessels. Many different conditions can cause low platelets by this mechanism. In the condition called idiopathic thrombocytopenic purpura, the immune system mistakenly breaks down platelets. Thrombotic thrombocytopenic purpura is a disease in which blood clots form in small blood vessels, which depletes platelets. In addition, bacteria in the blood, called sepsis, can also break down platelets.
References
- "Harrison's Principles of Internal Medicine"; Anthony S. Fauci et al; 17th Ed 2008
- "Robbins and Cotran Pathologic Basis of Disease"; Vinay Kumar et al.; 8th Ed 2009
