Contrast-Induced Nephropathy
Acute kidney injury occurring within 48-72 hours of intravascular iodinated contrast administration, defined as a rise in serum creatinine of ≥25% or ≥44 µmol/L from baseline. Risk is highest in patients with pre-existing CKD and diabetes. Prevention with IV hydration is the cornerstone of management.
Key Facts
Contrast-induced nephropathy (CIN) is defined as creatinine rise ≥25% or ≥44 µmol/L within 48-72 hours of contrast exposure Incidence: 1-2% in general population; 10-30% in high-risk patients (CKD + diabetes + heart failure) Most important risk factors: pre-existing CKD (eGFR <30), diabetes mellitus, volume depletion, concurrent nephrotoxins, large contrast volume Prevention is key: IV 0.9% NaCl 1mL/kg/hr for 12h pre and post (or 3mL/kg/hr for 1 hour pre if urgent); use lowest contrast volume Iso-osmolar (iodixanol) or low-osmolar contrast agents preferred over high-osmolar agents N-acetylcysteine: previously widely used; PRESERVE trial (2018) showed no benefit – now largely abandoned Stop metformin if eGFR <30 before contrast; restart 48 hours after if renal function stable Most cases are self-limiting: creatinine peaks at 3-5 days and returns to baseline within 7-14 days
Overview
Key Facts
CIN (also termed contrast-associated AKI, CA-AKI) is the third most common cause of hospital-acquired AKI. However, recent evidence suggests the true incidence may be lower than historically reported, as creatinine fluctuations may be coincidental.
Epidemiology
- General population: 1-2% incidence
- CKD (eGFR <60): 5-15%
- CKD + diabetes: 10-30%
- After primary PCI (emergency): up to 15-20%
- Higher with intra-arterial than intravenous contrast
Aetiology
- Iodinated contrast agents: ionic (diatrizoate) > non-ionic (iohexol, iopamidol) > iso-osmolar (iodixanol)
- Risk factors: CKD, diabetes, dehydration, heart failure, large contrast volume, concurrent nephrotoxins (NSAIDs, aminoglycosides), multiple myeloma
Pathophysiology
- Direct tubular toxicity: contrast causes oxidative stress, mitochondrial injury, and apoptosis of tubular cells
- Renal medullary hypoxia: contrast causes initial vasodilation then prolonged vasoconstriction of medullary blood vessels
- Osmotic effects: hyperosmolar contrast causes osmotic diuresis and tubular damage
- Tamm-Horsfall protein obstruction: contrast precipitates with proteins in tubular lumen
- Typically a non-oliguric AKI with peak creatinine at 3-5 days
Clinical Presentation
Typical Course
- Asymptomatic rise in creatinine within 48-72 hours of contrast
- Peak at 3-5 days
- Return to baseline within 7-14 days in most cases
- Usually non-oliguric
Severe Cases
- Oliguria: suggests more severe injury
- Need for dialysis: rare (<1% overall, but 3-5% in highest risk patients)
- Fluid overload: if AKI develops in heart failure patients
Red Flags
- Persistent or worsening creatinine beyond 7 days → consider alternative diagnosis (atheroembolic disease post-catheterisation)
- Cholesterol crystal emboli: livedo reticularis, blue toe syndrome, eosinophilia → atheroembolism after catheterisation
- Anaphylactoid reaction to contrast (immediate): urticaria, bronchospasm, hypotension → NOT CIN
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Atheroembolic disease | Livedo reticularis, eosinophilia, blue toes, occurs days-weeks post-catheterisation | Skin/renal biopsy, complement |
| Pre-renal AKI | Dehydration, hypotension, responds to fluids | Fluid challenge, urine Na |
| Allergic interstitial nephritis | Drug exposure, rash, eosinophilia | Urinalysis, biopsy |
| Cardiorenal syndrome | Post-PCI heart failure, fluid overload | BNP, echo |
| Coincidental AKI | Sepsis, other nephrotoxin | Full AKI workup |
Diagnosis / Investigation
Bloods
- Baseline creatinine: before contrast (essential)
- Creatinine at 48-72 hours: diagnostic comparison
- eGFR: risk stratification
- Serial creatinine: every 24-48 hours until stable
- Potassium: hyperkalaemia risk
Risk Assessment
- Mehran risk score (for PCI patients): estimates CIN risk based on hypotension, IABP, CHF, age, anaemia, diabetes, contrast volume, creatinine
- eGFR-based risk: <30 = high risk, 30-45 = moderate risk, >60 = low risk
Urine
- Urinalysis: bland sediment (unlike GN)
- Fractional excretion of sodium: may be low initially (pre-renal component) then >2% (ATN pattern)
Management
Prevention (Most Important)
All patients receiving iodinated contrast:
- Risk assessment: eGFR, diabetes status, hydration, concurrent medications
- Use lowest possible contrast volume (aim <3-4 mL/kg)
- Use low-osmolar or iso-osmolar contrast (avoid high-osmolar agents)
High-risk patients (eGFR <30, or <45 with diabetes):
- IV 0.9% NaCl: 1mL/kg/hr for 12 hours before and 12 hours after contrast
- If urgent: 3mL/kg/hr for 1 hour before + 1mL/kg/hr for 6 hours after
- Sodium bicarbonate 1.26%: some evidence of benefit; can be used as alternative (150mL/hr for 1 hour pre then 50mL/hr for 6 hours post)
Medication adjustments:
- Stop metformin: if eGFR <30 (48 hours before if elective); restart 48 hours after if creatinine stable
- Hold NSAIDs: before and after contrast
- Avoid concurrent nephrotoxins: aminoglycosides, ACEi/ARBs on day of contrast (some centres)
No longer recommended:
- N-acetylcysteine: PRESERVE trial (2018, NEJM) showed NO benefit → largely discontinued
- Mannitol/dopamine: no evidence of benefit
Treatment (If CIN Develops)
- Supportive: maintain hydration, monitor electrolytes
- Avoid further nephrotoxins
- Dialysis: rarely needed; indications as per standard AKI management
Referral Criteria
- CIN with dialysis requirement → nephrology
- Persistent renal impairment beyond 2 weeks → investigate for alternative diagnosis
- Recurrent need for contrast in CKD patients → nephrology/radiology MDT
Prognosis
- Most cases self-limiting: creatinine returns to baseline within 7-14 days
- Dialysis requirement: <1% overall; 3-5% in highest risk group
- In-hospital mortality: increased 5-10 fold when CIN develops (related to underlying comorbidities)
- Long-term CKD risk: controversial; CIN may accelerate pre-existing CKD progression
- PRESERVE trial: landmark study showing NAC and NaHCO3 are no better than saline alone
Other Relevant Information
CIN Prevention Summary
| Intervention | Evidence | Recommendation |
|---|---|---|
| IV 0.9% NaCl | Strong | Standard of care |
| Low/iso-osmolar contrast | Strong | Standard of care |
| Low contrast volume | Strong | Standard of care |
| NAC | PRESERVE trial – no benefit | Not recommended |
| NaHCO3 | PRESERVE trial – no additional benefit over NaCl | Not superior to NaCl |
| Mannitol | No evidence | Not recommended |
| Dopamine | No evidence | Not recommended |
Risk Stratification
| eGFR | Risk Level | Action |
|---|---|---|
| >60 | Low | Standard care |
| 45-59 | Low-moderate | Ensure hydration |
| 30-44 | Moderate | IV fluids, monitor creatinine |
| <30 | High | IV fluids 12h pre/post, lowest volume, consider alternatives (MRI, USS) |