This study will follow 2500 prevalent Chronic Kidney Disease (CKD) patients with Glomerular Filtration Rate (GFR) from 15-45 ml/min for 30 months with serial measurements every 6 months and subsequent annual chart review up to 60 months. This observational study will analyze the demographics, clinical status, medications and blood and urine samples of these patients and study the conventional biochemical, hormonal and metabolic parameters assessing which underlying biomarkers reflect the processes involved with disease progression.