If the patient has lived with a low Hb level, <9 for a long time, this may be caused by extramedullary hematopoiesis (EMH), which is the body responding to low Hb levels by producing masses of red blood cells outside the bone marrow, usually in the thoracic cavity. When the mass is next to or inside the lungs, it can affect the ability of the lungs to fully expand, causing an asthma like condition. This can result in fluid around the lungs and a high white cell count. If the doctors have not found an answer, EMH should be investigated. The best treatment is maintaining a higher Hb level. The doctor from Los Angeles Children's Hospital, one of the best thal centers on earth, told me that they maintain an Hb of above 11 when this problem occurs. Only by raising the Hb will these masses stop growing and shrink.