C3 and diabetic kidney disease: <h4>Objective</h4>To investigate the association between serum complement component 3 (C3) levels and renal pathological injury across different estimated glomerular filtration rate (eGFR) strata in patients with diabetic kidney disease (DKD) and evaluate its potential as an early-warning biomarker.<h4>Methods</h4>This retrospective study enrolled 187 DKD patients.