Background: Relative to hemoglobin A1c (HbA1c), glycated albumin (GA) more accurately reflects recent glycemic control in diabetic patients on hemodialysis and peritoneal dialysis. These assays have yet to be compared in patients with advanced chronic kidney disease (CKD). Methods: HbA1c and GA were simultaneously measured in 303 diabetic subjects: 70 with CKD prior to dialysis (CKD-stage 4), 184 with CKD after transplantation (TXP-stage 3) and 49 non-nephropathy controls. Results: Mean estimated GFR was 76, 46 and 26 ml/min in controls, TXP-3 and CKD-4 cases, respectively. Mean (SD) HbA1c (%) and GA (%) concentrations were 7.30 (1.40) and 16.8 (4.9) in controls, 7.28 (1.66) and 21.5 (6.4) in CKD-4 cases, and 7.21 (1.62) and 21.2 (5.5) in TXP-3 cases, respectively. The GA:HbA1c ratio differed significantly between non-nephropathy controls and both groups of CKD patients (both p < 0.001), but not between CKD-4 and TXP-3 cases (p = 0.92). The glucose:HbA1c ratio was inversely associated with GFR in all 254 nephropathy cases (r = –0.13; p = 0.04), while glucose:GA did not vary significantly based upon GFR (r = –0.08; p = 0.24). Conclusions: The relationship between glycated albumin and HbA1c is influenced by the presence of reduced GFR in diabetic patients with CKD. The accuracy of the HbA1c assay in diabetic subjects with severe nephropathy requires further investigation, although HbA1c performs relatively well with milder CKD.