BACKGROUND: Contrast-induced nephropathy (CIN) remains a serious complication following percutaneous coronary intervention (PCI), often leading to poor outcomes. Although the overall incidence of CIN is low, the risk can be significantly higher in certain susceptible cohorts. RESULTS: This prospective observational analytic study enrolled 174 consecutive eligible patients. The study selectively included diabetic patients with heart failure who are receiving regular diuretic therapy, being scheduled for elective coronary angiography (CAG) and/or PCI. CIN occurred in 24.7% of the study participants. CIN patients had significantly higher baseline osmolarity compared to those who did not develop CIN. After adjusting for other factors, pre-procedure osmolarity ≥ 302.3 mOsm/L, higher CHA CONCLUSIONS: In patients at high risk for CIN, serum osmolarity can serve as a practical stratification tool for CIN risk before elective CAG or PCI. Future studies should evaluate whether targeting a specific pre-procedural osmolarity threshold can reduce the risk of post-PCI CIN.