Combined residual inflammation and anemia in relation to kidney function among adults with diabetes: a CHARLS-based cross-sectional and longitudinal study

The combined phenotype of residual inflammation and anemia on kidney function in diabetes remains unclear. Our study examined their joint association with impaired kidney function and kidney function decline in a nationally representative Chinese sample. Our study encompassed 2,363 diabetes patients from the China Health and Retirement Longitudinal Study (CHARLS) for cross-sectional analysis and a sub-cohort of 547 patients for longitudinal analysis (2011–2015). Exposures comprised residual inflammation (hs-CRP ≥ 2.0 mg/L) and WHO-defined anemia. Outcomes were prevalent impaired kidney function in the cross-sectional analysis and rapid kidney function decline (RKFD) in the longitudinal analysis. Logistic and linear regression, restricted cubic splines, and subgroup and sensitivity analyses were applied. Cross-sectionally, isolated residual inflammation or isolated anemia were each associated with impaired kidney function, while the combined phenotype showed the strongest association (OR = 3.61, 95% CI: 2.16–5.99; P < 0.001). Longitudinally, this combined phenotype conferred the highest risk for RKFD (OR = 6.42, 95% CI: 2.18–18.34; P < 0.001) and was the only group associated with a steeper eGFR decline ( β= -8.68 mL/min/1.73 m², 95% CI: -15.72 to -1.64; P = 0.011). Sensitivity analyses and RCS models supported the robustness of these associations. Coexisting residual inflammation and anemia are associated with a higher prevalence of kidney function impairment and a more rapid kidney function decline among diabetic patients. Addressing both conditions concurrently as an integrated clinical phenotype may better mitigate kidney function decline. Not applicable.