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Contrast-associated acute kidney injury
A real risk of kidney injury from intravenous iodinated contrast exists mainly when eGFR is below 30 or there is AKI — these patients receive intravenous isotonic fluids, but a life-saving examination is never withheld.
Why it matters in the exam
Older literature called every creatinine rise after an examination "contrast-induced nephropathy" (CIN); controlled studies showed that many of these rises would have happened without contrast. Today we distinguish CA-AKI (kidney injury occurring after contrast) from CI-AKI (caused by it). According to the 2020 ACR–NKF consensus statement: eGFR 45 or more — negligible risk; 30–44 — individual decision; below 30, or AKI — real risk and prophylaxis should be considered. Intra-arterial injection with first-pass renal exposure (for example a catheter in the aorta above the renal arteries) carries a higher risk than intravenous injection.
Exam questions ask when to check creatinine before injection. The ACR recommends screening for age above 60, known kidney disease (dialysis, transplant, single kidney, renal surgery or tumour), treated hypertension, diabetes and patients taking metformin. Healthy young people without risk factors do not need a test. The KDIGO definition of AKI: a creatinine rise of 0.3 mg/dL or more within 48 hours, or a rise to 1.5 times baseline over 7 days, or urine output under 0.5 mL/kg/hour for 6 hours. After contrast the peak is usually at 2–5 days.
The only proven prophylaxis is intravenous isotonic fluid (0.9% saline), for example 1 mL/kg/hour for 6–12 hours before and 4–12 hours after, in a patient whose examination is not urgent and who is not fluid-overloaded. N-acetylcysteine and bicarbonate did not help (PRESERVE trial, 2018). Metformin: if eGFR is 30 or more and there is no AKI — no need to stop; if eGFR is below 30, there is AKI, or an arterial catheter study may send emboli to the kidneys — stop for 48 hours and recheck renal function. A dialysis patient does not need urgent dialysis after contrast unless there is fluid overload.
Key points
- Real risk — eGFR below 30 or AKI.
- Proven prophylaxis — intravenous isotonic fluids only.
- Pre-screening: age above 60, kidney disease, hypertension, diabetes, metformin.
- Metformin is stopped for 48 hours only with eGFR below 30, AKI or a risky arterial study.
- A life-saving examination is not delayed.
Summary table
| eGFR (mL/min/1.73 m²) | Risk | What to do | Metformin |
|---|---|---|---|
| 45 or more | Negligible | Inject as usual | Continue |
| 30–44 | Low; individual decision | Consider fluids when other risk factors exist | Continue |
| Below 30, not on dialysis | Real | Isotonic fluids before and after; consider an alternative | Stop for 48 hours |
| AKI | Real | Postpone if possible; if urgent — inject | Stop for 48 hours |
| Chronic dialysis | In most cases no kidney function to protect | Inject; dialysis as scheduled | Not relevant |
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Sources
- ACR–NKF Consensus Statement: Use of Intravenous Iodinated Contrast Media in Patients With Kidney Disease, 2020 — Risk thresholds and prophylaxis
- ACR Manual on Contrast Media, 2024 — Post-contrast acute kidney injury; Metformin
- KDIGO Clinical Practice Guideline for Acute Kidney Injury, 2012 — Definition and staging; Contrast-induced AKI
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.