A 52-year-old man with chronic kidney disease (eGFR 35 mL/min/1.73 m²) undergoes coronary angiography. During the procedure, an iodinated contrast agent is administered. Which of the following is the most common adverse reaction to iodinated contrast media in this patient?

Explanation

## Most Common Adverse Reaction to Iodinated Contrast Media ### Contrast-Induced Nephropathy (CIN) **Key Point:** Contrast-induced nephropathy is the most common serious adverse effect of iodinated contrast media, particularly in patients with pre-existing renal impairment. **High-Yield:** CIN is defined as an increase in serum creatinine of ≥0.5 mg/dL or ≥25% from baseline within 48–72 hours after contrast administration, in the absence of other causes. ### Risk Factors for CIN | Risk Factor | Mechanism | |---|---| | Pre-existing renal disease (eGFR <60) | Reduced glomerular filtration; impaired contrast clearance | | Diabetes mellitus | Microvascular injury; reduced renal perfusion | | Dehydration | Increased contrast osmolality effect | | Advanced age (>65 years) | Age-related decline in renal function | | High contrast volume | Direct tubular toxicity | | Heart failure | Reduced renal perfusion | **Clinical Pearl:** In this patient with eGFR 35 mL/min/1.73 m², the risk of CIN is significantly elevated. Prophylaxis with IV hydration (0.9% saline 1 mL/kg/hr for 12 hours pre- and post-procedure) and use of iso-osmolar or low-osmolar contrast media (LOCM) are standard preventive measures. ### Pathophysiology of CIN 1. **Direct tubular toxicity** — contrast agents are directly nephrotoxic to proximal tubular epithelium 2. **Renal vasoconstriction** — initial vasodilation followed by prolonged vasoconstriction reduces renal blood flow 3. **Osmotic diuresis** — high osmolality of contrast draws fluid into tubular lumen, concentrating contrast further 4. **Oxidative stress** — generation of reactive oxygen species damages tubular cells 5. **Viscosity increase** — increased blood viscosity impairs microcirculation **Mnemonic: TOXIC** — Tubular damage, Osmotic diuresis, Vasoconstriction, Ischemia, Contrast concentration ### Incidence by Population - General population: 1–3% - Patients with eGFR <60: 10–15% - Patients with eGFR <30 + diabetes: 20–50% - This patient (eGFR 35): ~10–15% baseline risk **Tip:** Always calculate eGFR before contrast administration. If eGFR <30, consider alternative imaging modalities (ultrasound, MRI without gadolinium) or defer the procedure unless absolutely essential.