polycythemia rubra vera causespolycythemia rubra vera complicationspolycythemia rubra vera diagnosispolycythemia vera complicationsrubra verasecondary polycythemia verapolycythemia vera myelofibrosispolycythemia vera prognosispolycythemia vera will result indefine polycythemia veraprimary polycythemia verapolycythemia rubra