acs is a clinical diagnosis helped by at least one chest x-ray. in all other organs low oxygen causes widening of blood vessels. but the lung is a unique organ where blood vessels become narrower when oxygen is low. this unique problem makes the lung a major target of the disease. fever is the most common symptom of acs in children because infection is more common. in the adults circulating clots and broken pieces of bone marrow can also add to the blockage of vessels in the lung and lead to acs. acs can be partially treated by blood transfusion to dilute the sickled cells with some normal red blood cells. an even better treatment is a procedure called red blood cell exchange. automated apheresis machines can do rbc exchange.