# Iodinated contrast for CT: kidney function checks, kidney protection and metformin

Source: https://onco.cc/protocols/iodinated-contrast-kidney-and-metformin/  
OnCo record `iodinated-contrast-kidney-and-metformin` (Protocol). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Many cancer scans use a dye containing iodine. If your kidneys work normally the dye is very unlikely to harm them, and you do not need to stop eating or drinking beforehand. If your kidneys are known to be weak, the team checks a recent blood test, may give you fluid through a drip around the scan, and may ask you to pause metformin for two days.

## Summary

Risk is judged from the estimated glomerular filtration rate (eGFR). For intravenous contrast the threshold for extra care is an eGFR below 30 ml/min/1.73 m², or acute kidney injury (ESUR 2026, ACR/NKF 2020, NICE NG148 2024); intra-arterial injection with first-pass renal exposure lowers the ESUR threshold to 45. ESUR measures eGFR within 7 days for inpatients or the acutely ill and within 3 months otherwise; NICE uses an eGFR from the past 6 months, or screening questions when there is none, and proceeds without a blood test if the answers are negative and the person is stable. Emergency imaging is not delayed for kidney function (NICE 1.1.7 [2024]; ACR/NKF).

Prevention in at-risk patients is intravenous volume expansion with 0.9% saline or isotonic bicarbonate, which ESUR finds equally effective (Level of evidence A) and recommends for at-risk patients (Level B). ESUR gives regimens (saline 1 ml/kg/h for 3 to 4 hours before and 4 to 6 hours after, or bicarbonate 3 ml/kg/h for 1 hour before; Level D) and does not accept oral fluids alone (Level D); NICE encourages oral hydration for those at increased risk and considers IV fluids for inpatients at particularly high risk. ACR/NKF prefer saline. N-acetylcysteine, statins, vitamin C and prophylactic dialysis are not recommended (ESUR Level A or B). Use low- or iso-osmolar contrast at the lowest diagnostic dose and recheck eGFR at 48 hours in at-risk patients.

The guidelines differ on ACE inhibitors and angiotensin receptor blockers: ESUR says they need not be stopped (Level B); NICE says consider stopping them temporarily when eGFR is below 30 [2013, amended 2024]. ESUR found insufficient evidence to withhold nephrotoxic chemotherapy before contrast (Level C). Metformin continues unless eGFR is below 30, there is acute kidney injury, or the injection is intra-arterial with first-pass renal exposure; then it stops at the time of contrast and restarts after an eGFR check at 48 hours (ESUR Level D; ACR/NKF agrees at eGFR below 30). People with myeloma and normal kidney function are not at higher risk if well hydrated; Bence Jones testing beforehand is not recommended (ESUR 2026). Fasting before low- or iso-osmolar contrast is not recommended (ESUR 2026).

## Fields

- Kind: Protocol
- Last checked: 2026-11-11
- Also known as: contrast nephropathy prevention; contrast-induced nephropathy; contrast-associated acute kidney injury; CA-AKI; PC-AKI; CT contrast and kidneys; eGFR before CT; metformin and contrast; IV hydration before CT

## Connected records

- protocols: [Contrast scans after a previous contrast reaction: allergy referral, switching agent and premedication](https://onco.cc/protocols/contrast-reaction-history-and-premedication/), [Gadolinium contrast for MRI in kidney impairment: NSF risk by agent group](https://onco.cc/protocols/gadolinium-contrast-kidney-impairment/), [Radiotherapy planning scan (CT simulation): positioning, skin marks and what the patient does](https://onco.cc/protocols/radiotherapy-planning-ct-simulation/)
- cancers: [Multiple myeloma](https://onco.cc/cancers/multiple-myeloma/)
- technologies: [CT (computed tomography)](https://onco.cc/technologies/ct/), [Iodinated and barium contrast for CT and X-ray](https://onco.cc/technologies/iodinated-contrast-media/)
- ideas: [Contrast CT booked on three kidney screening questions, without a routine blood test beforehand](https://onco.cc/ideas/idea-pu-contrast-ct-screening-questions/), [Eating and drinking normally before a contrast CT scan](https://onco.cc/ideas/idea-pu-no-fasting-before-contrast/)

---
JSON: https://onco.cc/api/v1/entities/iodinated-contrast-kidney-and-metformin.json