The study never started due to zero enrolment

The purpose of this study is to assess the presence of anti erythropoietin antibodies (anti EPO Ab) in participants responding to any erythropoietin receptor agonist (ERA) therapy to treat or prevent anemia without loss of effectiveness to see if they will develop pure red cell aplasia or loss of effectiveness to recombinant erythropoietin and to measure the duration of effectiveness of ERA therapy.

This is an observational (study in which the investigators/physicians observe the participant's data and measure their outcomes), international, multicenter (study conducted at multiple sites), cohort (group of individuals with similar characteristics) study. The study consists of prestudy phase, observational phase (2 years), and follow-up phase (1 year). Approximately 50 participants who already receiving ERA therapy for anemia will be observed in this study. In the observational phase, participants' erythropoietin antibody status (positive or negative), clinical progress, treatment for anemia or prevention of anemia, and outcome will be monitored. During this study, enrolled participants will continue to receive standard-of-care treatment for their disease from their individual investigators as before enrollment to this study. Safety evaluations will include assessment of adverse events which will be monitored throughout the study. The total duration of the study will be 3 years.

Inclusion Criteria:

• Receiving any ERA therapy for any cause of anemia and having responded to the ERA therapy for at least 3 months
• Positive or borderline serum for antibodies to erythropoietin identified by serum radioimmunoprecipitation
• Maintained a stable hemoglobin within a 3-month period that has not decreased more than 2 g/dL in any 1-month period and with no increase in red blood cell transfusion requirement
• An ERA maintenance dose that has not increased more than 50 percentages from initial effective dose
• If blood count information is available, must have a count of reticulocytes (immature red blood cells) greater than or equal to 30 million/L

Exclusion Criteria:

• Stem cell or bone marrow transplantation
• Treatment with medication that decreases the ability of the immune system to function normally, within the last 3 months
• Participants who have shown a loss of effectiveness to ERA therapy, defined as participants who initially responded to treatment for anemia [a rise in hemoglobin which lasted for a minimum of 3 months] followed by an unexplained decrease in hemoglobin (greater than or equal to 2 g/dL) within a 1-month period

Participants with positive or borderline serum anti erythropoietin antibody titer and who are responding to any erythropoietin receptor agonist (ERA) therapy for any cause of anemia