Iron therapy was significantly associated with CKD progression (defined as eGFR ≤ 30 mL/min/1.73 m2) in patients aged ≥ 65 years (hazard ratio, 1.761, 95% CI, 1.291 to 2.403), those with CRP ≥10 mg/L (hazard ratio 1.379, 95% CI, 1.041 to 1.828), diabetes mellitus (hazard ratio 1.421, 95% CI, 1.180 to 1.711), GFR <45 mL/min/1.73 m2 (hazard ratio 3.839, 95% CI, 2.986 to 4.935), aged ≥ 65 years (hazard ratio 1.51, 95% CI, 1.277 to 1.859), and serum albumin < 3.5 g/dL (hazard ratio 1.383, 95% CI, 1.101 to 1.738) (Figure 3D). Here, CRP is linked to chronic kidney disease.