Contrast Associated Acute Kidney Injury

Contrast-associated acute kidney injury (CA-AKI) is a rise in creatinine of 0.3 mg/dL or more (or 1.5 times baseline) within 48 to 72 hours after intravascular iodinated contrast. Contrast-induced nephropathy refers to the causal subset.

• Incidence 1 to 2% in the general population receiving IV contrast with normal renal function; up to 20 to 50% in high-risk patients undergoing intra-arterial contrast.
• Risk factors: eGFR under 45 (strongest under 30), diabetes, heart failure, hypovolaemia, hypotension, advanced age, anaemia, high contrast volume, intra-arterial administration, nephrotoxic drugs, myeloma.
• Mechanism: renal vasoconstriction with medullary hypoxia, direct tubular toxicity, oxidative stress.
• Course: creatinine peaks at 3 to 5 days, returns to baseline in 7 to 14 days; permanent loss in few; dialysis rarely required.
• Mehran score stratifies risk after PCI.

• Usually asymptomatic; non-oliguric in most; oliguria in severe cases.
• Rising creatinine with bland sediment or granular casts, low fractional excretion of sodium (under 1%) early.
• Peripheral oedema, hyperkalaemia, acidosis in severe injury.
• Distinguish from cholesterol embolisation (delayed over weeks, livedo, eosinophilia), ATN from other causes, AIN.

• Baseline creatinine and eGFR before contrast in at-risk patients; repeat at 48 to 72 hours.
• Diagnosis by KDIGO criteria and timing; urinalysis (granular casts), urine sodium, renal ultrasound to exclude obstruction.
• Exclude other causes (sepsis, hypotension, drugs, atheroembolism).
• Risk assessment: eGFR, diabetes, heart failure, contrast volume, Mehran score.

Prevention (essential)

• Assess necessity of contrast; use alternatives (non-contrast CT, ultrasound, MRI with caution) when possible.
• For eGFR under 30 (or under 45 with intra-arterial first-pass exposure): IV isotonic saline 1 mL/kg/h for 6 to 12 hours before and 6 to 12 hours after contrast (0.5 mL/kg/h if ejection fraction under 35% or heart failure), or LVEDP-guided hydration during angiography.
• Use iso-osmolar or low-osmolar contrast at the lowest volume possible (contrast volume to eGFR ratio under 2 to 3), avoid repeat exposure within 72 hours.
• Hold nephrotoxic drugs (NSAIDs, aminoglycosides), diuretics, and metformin if eGFR under 30 or AKI (restart at 48 hours after confirming stable creatinine).
• High-intensity statin loading (atorvastatin 40 to 80 mg) offers modest benefit.
• Sodium bicarbonate and N-acetylcysteine have no proven added benefit.

Treatment

• Supportive: euvolaemia, avoid further nephrotoxins, adjust drug doses, treat hyperkalaemia and acidosis.
• Renal replacement therapy for standard indications; prophylactic dialysis or haemofiltration after contrast is not beneficial.
• Follow creatinine until recovery, and at 3 months to detect CKD.