In certain aspects, the present invention provides compositions and methods for increasing red blood cell and/or hemoglobin levels in vertebrates, including rodents and primates, and particularly in humans.在某些方面中,本發明提供在脊椎動物(包括齧齒動物及靈長類動物,且尤其人類)中增加紅血球及/或血紅素水平的組成物及方法。