Ascertain the Optimal Starting Dose of Mircera Given Subcutaneously for Maintenance Treatment of Anemia in Pediatric Patients With Chronic Kidney Disease on Dialysis or Not Yet on Dialysis.

Inclusion Criteria: * Pediatric participants 3 months to 17 years of age with clinically stable chronic renal anemia * CKD with estimated glomerular filtration rate (eGFR) of \< 45 mL/min/1.73 m2 (determined by the Bedside Schwartz formula) or dialysis treatment for at least 8 weeks before the first dose of Mircera * For participants on peritoneal dialysis (PD): a weekly Kt/V≥ 1.8 * For participants on hemodialysis (HD): adequate HD, urea reduction ratio (URR) \> 65% or Kt/V \> 1.2 for participants on HD three times per week. Participants with fewer than or more than three HD sessions per week should have a weekly Kt/V≥ 3.6. * Baseline Hb concentration 10.0-12.0 g/dL determined from the mean of two Hb values measured at Visit 1 (Week -3) and Visit 2 (Week -1) * Stable SC maintenance treatment with epoetin alfa, epoetin beta, or darbepoetin alfa with the same dosing interval for at least 6 weeks before the first dose of Mircera * Stable dose of epoetin alfa, epoetin beta, or darbepoetin alfa treatment with no weekly dose change \> 25% (increase or decrease) for at least 4 weeks before the first dose of Mircera * Adequate iron status defined as ferritin≥100 ng/mL or transferrin saturation (TSAT)≥ 20% (or percentage of hypochromic red cells \< 10%); mean of two values measured during screening. Exclusion Criteria: * Overt gastrointestinal bleeding within 8 weeks before screening or during the screening period * RBC transfusions within 8 weeks before screening or during the …