A rapid and simple assay to determine pegylated erythropoietin in human serum

Stimulation of erythropoiesis by the third-generation erythropoietin drug, continuous erythropoietin receptor activator (CERA), a pegylated derivative of epoetin-beta, has provided valuable therapeutic benefits to patients suffering from renal anemia, but has also rapidly found application as an illicit performance-enhancing strategy in endurance sports. We present here a novel method for selective determination of CERA in serum, based on polyethylene glycol precipitation, followed by a commercial homogeneous immunoassay. The developed method was highly discriminating between serum samples from CERA-treated patients and control subjects, as the covalently linked polyethylene glycol chain in CERA strongly enhanced the solubility of the protein in a polyethylene glycol-containing medium. Intravenous administration of CERA could be detected for several weeks in the majority of subjects tested. This assay outperforms the currently available CERA detection methods in terms of simplicity, convenience, cost, and throughput, making it ideal as a screening tool for doping control.