Active Vitamin D Level Is Independently Associated with the Presence and Severity of Coronary Artery Disease in Patients with Chronic Kidney Disease

<i>Background and Objectives:</i> Chronic kidney disease (CKD) increases the risk of coronary artery disease (CAD), and vitamin D deficiency-particularly reduced levels of 1,25-dihydroxyvitamin D [1,25(OH)₂D], the biologically active form of vitamin D that declines early in CKD due to impaired renal conversion-may be a contributing factor. This study aimed to assess the relationship between 1,25(OH)₂D levels and the presence and severity of CAD in CKD patients. <i>Materials and Methods:</i> We retrospectively analyzed 398 non-dialysis CKD patients (eGFR < 60 mL/min/1.73 m²) who underwent elective coronary angiography. Serum 1,25(OH)₂D and 25(OH)D levels were measured, and CAD severity was assessed using the Gensini score. <i>Results:</i> Lower 1,25(OH)₂D levels were independently associated with both the presence and se-verity of CAD. Logistic regression revealed that each 1 pg/mL increase in 1,25(OH)₂D was linked to an 11% reduction in odds of significant CAD (OR: 0.89; 95% CI: 0.86-0.93; <i>p</i> < 0.001). In contrast, 25(OH)D was not significantly related to CAD. Linear regression showed an inverse correlation between 1,25(OH)₂D and Gensini scores (β = -0.329, <i>p</i> < 0.001), indicating reduced disease severity with higher vitamin D levels. Subgroup analyses confirmed consistent associations across age, sex, diabetes, hypertension, and LDL-cholesterol categories. ROC analysis demonstrated that 1,25(OH)₂D alone had good predictive ability for CAD (AUC = 0.818), which improved to 0.925 when combined with traditional risk factors. The optimal cutoff for 1,25(OH)₂D was ≤16.6 pg/mL, yielding 73.3% sensitivity and 83.5% specificity. <i>Conclusions</i>: Serum 1,25(OH)₂D is an independent predictor of both the presence and extent of CAD in CKD patients and may serve as a valuable non-traditional biomarker for cardiovascular risk assessment.