Definitions and uncertainty
Traditional Definition
- Creatinine ↑ ≥26 µmol/L OR ≥50% from baseline within 48-72 h of contrast
Problems With This Definition
- Background AKI risk in unwell hospitalised patients is high regardless of contrast
- Many 'CIN' cases would have happened anyway (sepsis, hypotension, drugs)
- Studies with control groups (non-contrast CT in matched patients) show very small attributable risk
Modern Terminology
- Post-contrast AKI (PC-AKI) — any AKI after contrast, regardless of cause
- Contrast-induced AKI (CI-AKI) — AKI causally attributable to contrast (rarely provable)
MECHANISM (when it does occur):
- Direct tubular toxicity (osmotic stress)
- Renal medullary vasoconstriction → ischaemia
- Generation of reactive oxygen species
Risk stratification
High Risk
- eGFR <30 mL/min/1.73 m²
- Diabetes WITH CKD
- Heart failure (low EF, congestive)
- Hypovolaemia / hypotension at time of contrast
- Sepsis
- Multiple nephrotoxins (NSAIDs, aminoglycosides, amphotericin)
- Older age (>75)
- High volume contrast (>5 mL per kg)
- Repeat contrast within 48-72 hours
- INTRA-ARTERIAL contrast (cardiac cath, peripheral angio)
Low Risk
- eGFR ≥30 with single IV contrast study
- Outpatient, euvolaemic
- Modern low/iso-osmolar contrast
Dialysis Patients
- Anuric dialysis patients — contrast safe, no extra dialysis needed
- Residual kidney function — protect it; use minimum dose; hydrate; standard dialysis schedule (no urgent post-contrast HD)
Kidney Vitality is a daily multivitamin developed by a UK Consultant Nephrologist using renal nutrition principles. It contains no added potassium, magnesium, phosphorus or iron, and no herbal blends. See the formulation.
Prevention — what works and what doesn't
Proven
- IV ISOTONIC FLUID (0.9% saline OR sodium bicarbonate isotonic — both equivalent per PRESERVE)
- 1 mL/kg/hr for 6-12 h before and 6-12 h after
- Outpatient: 3 mL/kg over 1 h before + 1 mL/kg/hr for 6 h after
- Caution in heart failure — individualise; sometimes minimal hydration is wisest
- STOP NEPHROTOXINS 48 h before:
- NSAIDs
- Aminoglycosides if possible
- Diuretics in volume-depleted patients
- Metformin (per MHRA): stop on day of contrast if eGFR <60, restart 48 h later after rechecking eGFR
- SGLT2 inhibitors: stop on day of contrast (sick-day rule)
- USE LOWEST POSSIBLE CONTRAST VOLUME
- AVOID REPEAT contrast within 48-72 h
ABANDONED (no benefit):
- N-acetylcysteine (NAC)
- Sodium bicarbonate IV beyond hydration
- Statins around contrast
- Ascorbic acid
- Fenoldopam, theophylline
- Periprocedural haemofiltration
- Mannitol
Gadolinium-based Contrast (Mri)
- Different concern — nephrogenic systemic fibrosis (NSF)
- Group I agents (older linear chelates) AVOID in eGFR <30
- Group II agents (macrocyclic — gadobutrol, gadoteridol) safe in low eGFR
- Single dose macrocyclic in eGFR <30 acceptable when needed
Practical guidance
Before Contrast
- Check eGFR within previous 3 months (any time-frame if AKI risk)
- Risk stratify (KDIGO + ESUR criteria)
- Hydrate high-risk patients (see above)
- Withhold nephrotoxins where possible
- Document the discussion when contrast is needed in CKD
During
- Lowest osmolar agent
- Smallest dose for diagnostic question
After
- Check creatinine 48-72 h if outpatient was high-risk
- Maintain hydration
- Restart withheld meds at appropriate time (metformin after 48 h if creatinine stable)
Key Message
Do NOT withhold essential contrast imaging in a critically ill patient on theoretical CIN grounds. The diagnostic value of the scan almost always outweighs the small risk of AKI. Optimise hydration and proceed.
When To Refer To Nephrology
- AKI ≥ stage 2 (creatinine doubling)
- AKI persisting beyond 7 days
- Need for ongoing contrast studies in patient with established CKD
