A reduction in blood platelets is usually caused by conditions that decrease production of platelets or increase the consumption or destruction of platelets, according to MedicineNet.com. Reduction of platelets are also caused by increased splenic sequestration, a condition occurring when circulating platelets become trapped in the spleen.
A decrease in the production of blood platelets is typically associated with problems involving bone marrow, reports MedicineNet.com. Viral infections such as HIV, varicella or chickenpox, rubella, mumps, or hepatitis C adversely affect bone marrow, causing reduced platelet production. Medications such as thiazide diuretics and chemotherapy drugs and also the long-term consumption of alcohol are other causes of diminished platelet production by bone marrow.
A number of medications cause an immune system reaction against platelets, asserts MedicineNet.com. Drugs associated with immune-related destruction of blood platelets include sulfonamide antibiotics, acetaminophen, quinine and heparin. Blood transfusions and organ transplants can also trigger immune responses, causing lowered numbers of platelets.
Thrombotic thrombocytopenic purpura and a related condition called hemolytic uremic syndrome are nonimmune conditions that can cause increased consumption of platelets, states MedicineNet.com. These conditions result from pregnancy, infections, chemotherapy and metastatic cancers. The body's consumption of platelets is also increased by trauma and sepsis. Blood vessel injury or inflammation and artificial heart valve replacements are sometimes responsible for the destruction of blood platelets.