The Role of Urine Specific Gravity in Predicting Contrast-Induced Nephropathy in Patients Undergoing Coronary Angiography: A Prospective Study

Objective: To investigate the relationship between preprocedural urine specific gravity (USG) and contrast-induced nephropathy (CIN) in patients undergoing coronary angiography (CAG) and to evaluate its role in risk prediction.
Method: This prospective study included 191 consecutive patients undergoing CAG. USG was measured 30 minutes before the procedure. CIN was defined as a ≥25% increase from baseline or an absolute increase of ≥0.5 mg/dL in serum creatinine 48–72 hours after the procedure. Factors predicting the development of CIN were analyzed using univariate and multivariate logistic regression analyses.
Results: The median age of the study population was 63.0 years (IQR: 55.0–71.0), and CIN developed in 33 patients (17.3%). Preprocedural USG was significantly higher in the CIN(+) group than in the CIN(−) group (1020.9±5.4 vs. 1017.7±6.6; P =.002). Multivariate analysis identified USG (OR: 1.10, 95% CI: 1.02–1.18; P =.010), non-ST-segment elevation myocardial infarction (NSTEMI) (OR: 3.32, 95% CI: 1.33–8.25; P =.010), New York Heart Association (NYHA) Class III/IV (OR: 15.90, 95% CI: 2.76–91.50; P =.002), and bundle branch block (OR: 6.60, 95% CI: 1.78–24.42; P =.005) as independent predictors of CIN. The area under the curve (AUC) for USG was 0.671. At a cutoff value of 1017, USG demonstrated 81.8% sensitivity, 53.2% specificity, and a 93.3% negative predictive value (NPV). Although its overall discriminatory performance was similar to that of the Mehran risk score, USG exhibited a complementary diagnostic profile.
Conclusion: Elevated preprocedural USG is an independent risk factor for CIN. Given its high NPV, USG may serve as a modest, noninvasive, complementary bedside tool for risk stratification. The observed independent association between bundle branch block and CIN should be regarded strictly as hypothesis-generating and requires confirmation in larger cohorts.

Keywords: Acute kidney injury, contrast-induced nephropathy, coronary angiography, dehydration, urine specific gravity.