A 62-year-old man with chronic kidney disease (eGFR 35 mL/min/1.73m²) requires contrast-enhanced CT angiography. Which contrast agent is most appropriate to minimize the risk of contrast-induced nephropathy (CIN)?

Explanation

## Contrast Selection in Renal Impairment **Key Point:** In patients with reduced renal function, iso-osmolality contrast media (IOCM) are preferred over low-osmolality (LOCM) and high-osmolality (HOCM) agents to minimize contrast-induced nephropathy (CIN) risk. ### Contrast Media Safety Hierarchy in CKD | Osmolality Class | Agent | Osmolality | CIN Risk | Recommendation | |------------------|-------|-----------|----------|----------------| | **Iso-osmolality (IOCM)** | **Iodixanol** | **≈290** | **Lowest** | **Preferred in eGFR <30** | | Low-osmolality (LOCM) | Iohexol, Iopamidol, Ioversol | 600–850 | Intermediate | Acceptable if adequate hydration | | High-osmolality (HOCM) | Diatrizoate, Meglumine salts | 1400–2400 | Highest | **Contraindicated in CKD** | ### Pathophysiology of CIN 1. **Osmotic diuresis** → reduced renal perfusion 2. **Direct tubular toxicity** → epithelial cell injury 3. **Reactive oxygen species** → oxidative stress 4. **Renal medullary hypoxia** → ischemic injury **HOCM agents amplify all these mechanisms** through their high osmolality, making them unsuitable in CKD. **High-Yield:** Iodixanol (IOCM) has osmolality equal to plasma (~290 mOsm/kg), eliminating osmotic gradient-driven fluid shifts and renal medullary dehydration. Recent meta-analyses show IOCM ≤ LOCM in CIN prevention, but IOCM is still preferred in severe renal impairment (eGFR <30). **Clinical Pearl:** In this case, eGFR 35 is stage 3b CKD. Iodixanol is the safest choice. Adequate hydration (0.9% saline) and minimizing contrast volume are equally important preventive measures. **Mnemonic:** **IOCM in CKD** — Iso-Osmolality Contrast Media in Chronic Kidney Disease = gold standard.