Recombinant erythropoietins are effective in treating anemia caused by many diseases, including chronic renal disease. Pure red cell aplasia (PRCA, a rare form of anemia) and the development of antibodies to erythropoietin have been reported to occur infrequently in patients who are being treated with recombinant erythropoietins. The incidence of PRCA and antibody development is unknown. In this observational study, the clinical course and outcome of patients with a diagnosis of PRCA associated with current or past recombinant erythropoietin use that have experienced a loss of effectiveness of erythropoietin will be followed for a period of up to 4 years. During the study, no treatment will be specified and no medication will be supplied by the Sponsor of the study (Johnson and Johnson Pharmaceutical Research and Development, LLC). Patients will be treated by their individual physicians for PRCA and study visits will be timed to coincide with regularly scheduled standard-of-care visits for PRCA. Blood-sampling for study-specific tests will be done with routine standard-of-care laboratory evaluations. Information relating to PRCA treatments, clinical course and outcome, risk factors for loss of effectiveness and adverse events will be collected at each visit. Blood tests to determine the presence or absence of erythropoietin antibodies will be performed. Safety will be assessed throughout the study by recording adverse events, including complications of red blood cell transfusions and any new diagnoses of cancer, blood or immune system diseases or hormone deficiency which are identified through the course of the patients' regular treatment and care for PRCA. Historical information will also be collected for all patients participating in the study, including previous recombinant erythropoietin treatment dates, number of transfusions, medications, dialysis and transplantation history, from a period of 1 year before the date of loss of effectiveness of erythropoietin to the start date of the study. Previous information for patients who have died or who do not consent to participate in the observational study but do consent to allow their previous data to be reviewed will be collected. Patients may also participate in an optional portion of the study in which their genetic material will be analyzed to see if it contains something that would cause their immune system to make antibodies to erythropoietin. The study hypothesis is that a possible relationship exists between erythropoietin antibodies and the clinical course and outcome of patients with PRCA in patients currently or previously treated with recombinant erythropoietin.

Since the study is purely an observation of patients with PRCA, no treatment will be required by the Sponsor and no medication will be supplied by the Sponsor. Patients will receive standard-of-care treatment from their individual physicians.