Platelets are created in the bone marrow, which also contains the raw materials for oxygen-carrying red blood cells and infection-fighting white blood cells. An important component of blood clot formation, platelets are stored in the spleen. Eventually, the liver and spleen destroy old platelets. Normally, there are 150 billion to 450 billion platelets per microliter of blood, according to the Mayo Clinic. High platelet count, or thrombocytosis, may be a symptom of an underlying condition.
Acute Conditions
Reactive, or secondary, thrombocytosis seldom causes symptoms. The increase in platelets may be due to the body's response to healing crisis and inflammation, such as recent surgery. A poorly functioning spleen or having had the spleen surgically removed can account for high platelets in the blood, but complications such as the formation of clots in deep veins (thrombosis) are rare, and the liver may be able to compensate. Serious blood loss or iron deficiency anemia also may trigger reactive thrombocytosis. Platelet count may rise in response to bacterial infections of the blood or urinary tract or in conditions such as pneumonia, meningitis and septic arthritis. High platelets can be a feature of Kawasaki disease, an illness that primarily strikes young children of Asian descent.
MPDs
Essential, or primary, thrombocytosis may be caused by myeloproliferative diseases, or MPDs, a group of blood cancers affecting the bone marrow. The main types--polycythemia vera, primary myelofibrosis and essential thrombocytopenia--may progress to more serious conditions such as myelodysplastic syndrome and acute myeloid leukemia. MPD can strike adults and children. According to the MPD Foundation, these incurable diseases affect approximately 136,000 people in the United States.
Chronic Inflammatory Diseases
Thrombocytosis can be part of the clinical picture of rheumatoid arthritis and inflammatory bowel diseases, such as Chron's disease and ulcerative colitis. Elevated platelets are one of many abnormal laboratory findings that can be expected in celiac disease, characterized by an inflammatory reaction to dietary gluten that damages the small intestine. Gluten is a protein found in wheat, barley and rye. Strict avoidance of gluten-containing foods can completely resolve symptoms and is the only treatment for celiac disease. David Nelsen, M.D., of the University of Arkansas for Medical Sciences, explains in a 2002 report in "American Family Physician" that gluten intolerance may affect one in 250 persons, predominantly those of European descent.
Medications
Overuse of medications in the treatment of low platelet count can result in high platelets in the blood. Thrombocytosis also may be an uncommon side effect of antibiotics containing cephalosporin or amoxicillin, such as Cefizox or Augmentin, as well as the combination of piperacillin and tazobactam in Zosyn, used intravenously to treat serious infections.
