ORLANDO, Fla. — A drug made by Amgen maintained blood platelet counts in patients with an autoimmune bleeding disorder, according to results of a five-year study released Sunday.

Amgen announced results of its study of Nplate (romiplostim) in adults with chronic immune thrombocytopenic purpura, in which the body’s own immune system destroys platelets, necessary for clotting of the blood. Results of the study, which showed that 95% of the 292 patients receiving the drug maintained platelet counts, were presented at the annual meeting and exposition of the American Society of Hematology.

“In this study, nearly all Nplate-treated patients were able to maintain platelet counts within the target range for more than five years,” said David Kuter, lead study investigator and chief of hematology at Boston’s Massachusetts General Hospital.