An abnormally glycosylated isoform of erythropoietin in hemangioblastoma is associated with polycythemia.

Hemangioblastomas express erythropoietin and the patients often present with polycythemia.Serum erythropoietin was measured using a commercial immunoassay, a functional erythropoietin assay and iso-electric focusing.Despite the polycythemia, serum erythropoietin remained low, while a functional erythropoietin-assay showed a 4-5 higher activity in serum compared to the immunoassay. Iso-electric focusing of serum erythropoietin indicated overrepresentation of highly sialylated erythropoietin isoforms produced by the tumor. As a result, altered affinity of the monoclonal antibody used in the immunoassay for the hypersialylated isoforms was suggested.Analysis of erythropoietin isoforms may be helpful in distinguishing the ectopic erythropoietin isoforms from normally glycosylated erythropoietin.