blood counts are required on a regular basis to determine whether the patient is still in remission. many patients with aplastic anemia also have clones of cells characteristic of paroxysmal nocturnal hemoglobinuria (pnh), a rare disease that causes anemia with thrombocytopenia and/or thrombosis and is sometimes referred to as aa/pnh. occasionally pnh dominates over time, with the major manifestation of intravascular hemolysis. the overlap of aa and pnh has been speculated to be an escape mechanism by the bone marrow against destruction by the immune system. flow cytometry testing is performed regularly in people with previous aplastic anemia to monitor for the development of pnh. prognosis untreated, severe aplastic anemia has a high risk of death. modern treatment produces a five-year survival rate that exceeds 85%, with younger age associated with higher survival. survival rates for stem cell transplants vary depending on the age and availability of a well-matched donor. they are better for patients who have donors that are matched siblings and worse for patients who receive their marrow from unrelated donors. overall, the five-year survival rate is higher than 75% among recipients of blood marrow transplantation. older people (who are generally too frail to undergo bone marrow transplants) and people who are unable to find a good bone marrow match have five-year survival rates of up to 35% when undergoing immune suppression. relapses are common. relapse following atg/ciclosporin use can sometimes be treated with a repeated course of therapy. in addition, 10–15% of severe aplastic anemia cases evolve into myelodysplastic syndrome and leukemia. according to one study, 15.9% of children who responded to immunosuppressive therapy eventually relapsed. milder disease may resolve on its own. etymology aplastic is a combination of two ancient greek elements: a- (meaning "not") and -plasis ("forming into a shape"). anemia is a combination of the ancient greek element an- ("not") and -emia (neo-latin from the greek -(h)aimia, meaning "blood"). epidemiology aplastic anemia is a rare, noncancerous disorder in which the blood marrow is unable to adequately produce blood cells required for survival. it is estimated that the incidence of aplastic anemia is 0.7–4.1 cases per million people worldwide, with the prevalence between men and women being approximately equal. the incidence rate of aplastic anemia in asia is 2–3 times higher than it is in the west; the incidence in the united states is 300–900 cases per year. the disease most commonly affects adults aged 15–25 and over the age of 60, but it can be observed in all age groups. the disease is usually acquired during life and not inherited. acquired cases are often linked to environmental exposures such as chemicals, drugs, and infectious agents that damage the bone marrow and compromise its ability to generate new blood cells. however, in many instances the underlying cause for the disease is not found. this is referred to as idiopathic aplastic anemia and accounts for 75% of cases. this compromises the effectiveness of treatment since treatment of the disease is often aimed at the underlying cause. those with a higher risk for aplastic anemia include individuals who are exposed to high-dose radiation or toxic chemicals, take certain prescription drugs, have pre-existing autoimmune disorders or blood diseases, or are pregnant. no screening test currently exists for early detection of aplastic anemia. notable cases marie curie eleanor roosevelt donny schmit ted devita demetrio stratos john dill (british field marshal) robert mcfall (asbestos worker from pittsburgh who unsuccessfully sued his cousin for a transfusion of bone marrow)