This is a multicenter (study conducted at multiple sites), observational (study in which the investigators/physicians observe the participant's data and measure their outcomes) study. Approximately 150 participants will be enrolled in this study. The study consists of an initial observation phase and extended observation period. An initial observation phase starting at enrollment and ending when 24 months have elapsed since the date of loss of efficacy (LOE), supplemented with retrospective data collection for the period between LOE date and date of enrollment in the study. Participants remaining epoetin alfa (EPO-Ab) positive 24 months after LOE will enter a 2-year extended observation period. Study visits will take place every month during the initial observation phase and data will be collected every 6 months during the extended observation phase. Safety evaluations will include assessment of adverse events, clinical laboratory tests, vital signs, and physical examination which will be monitored throughout the study. The total study duration for each participant will be approximately for 4 years.