Skip to content

Draft: not yet reviewed by a clinician

Use this page to prepare questions for your care team. It does not replace their advice. Your own targets and doses come from your nephrologist, diabetes team and renal dietitian.

Scans, contrast dye and bowel preparations

No doses on this page

This handbook never gives insulin or medicine doses and never tells you to change one. Your prescriber sets every dose and every change, and writes down when to pause a medicine and when to restart it. A low blood glucose is always treated straight away: see Treating a low and Get help now.

In short

Many scans use a dye (contrast) to show blood vessels and organs more clearly. With kidney disease the worry is that the dye harms the kidneys. For dye given into a vein for a CT scan, that risk is much smaller than doctors once thought (ACR–NKF 2020). Do not refuse a scan you need because of your kidneys: missing a diagnosis can do more harm (KDIGO 2024, section 4.4). Tell the team ordering the scan about your kidney disease, your latest eGFR and your diabetes, so they can plan. Avoid sodium phosphate bowel preparations, and plan your insulin and glucose for any fasting.

Your numbers

Your situation What usually happens Source
CT dye into a vein, eGFR 45 or more no special steps for the kidneys ACR–NKF 2020
CT dye, eGFR 30–44 fluids through a drip may be given if your risk is high; the ordering doctor decides ACR–NKF 2020
CT dye, eGFR under 30, not on dialysis, or a sudden kidney injury fluids through a drip (saline) around the scan are advised ACR–NKF 2020
On dialysis an extra or earlier dialysis session after dye is not needed and may be harmful KDIGO 2024, section 4.4.1
MRI with gadolinium, eGFR under 30 or on dialysis the newer, lower-risk agents (ACR group II, or group III) are used KDIGO 2024, practice point 4.4.2.1; ACR–NKF 2021
Heart catheter (dye into an artery) risk is assessed separately with a scoring tool KDIGO 2024, practice point 4.4.1.1

eGFR is in mL/min/1.73 m². See eGFR and creatinine.

CT scans with iodine dye

  • The dye given into a vein for a CT scan is linked with kidney injury far less often than once thought, because older studies had no proper comparison groups (ACR–NKF 2020).
  • Diabetes adds to the risk when kidney function is already low, which is one more reason to tell the team about both (KDIGO 2024, Table 33).
  • If your eGFR is under 30 and you are not on dialysis, or you have a sudden kidney injury, the team should give you saline through a drip around the scan (ACR–NKF 2020). If you have heart failure or a fluid limit, ask how they will balance that.
  • If your eGFR is under 30 or you have a sudden kidney injury, KDIGO suggests stopping medicines that can harm the kidneys and are not essential, such as NSAIDs or diuretics, from 1–2 days before until 2 days after the dye. Before a planned CT with dye, your team may also hold an ACE inhibitor or ARB for 2 days (KDIGO 2024, section 4.4.1). Pause a medicine only if they tell you to, and get the restart date in writing.
  • Pills and drinks such as N-acetylcysteine or vitamin C have not been shown to protect the kidneys (KDIGO 2024, section 4.4.1).
  • On dialysis: you do not need an extra session after the dye (KDIGO 2024, section 4.4.1). If you still pass urine, ask how they will protect what kidney function you have left.

MRI with gadolinium

Gadolinium is the dye used for many MRI scans. Older types caused a rare, serious condition that thickens the skin and other tissues (nephrogenic systemic fibrosis) in people with very low kidney function. KDIGO notes that no cases have been reported after 2012 (KDIGO 2024, section 4.4.2). With the newer group II agents the risk is very low: there were no cases after 4,931 doses given to people with an eGFR under 30 (ACR–NKF 2021). KDIGO advises these lower-risk agents for anyone with an eGFR under 30 (KDIGO 2024, practice point 4.4.2.1). Delaying a needed MRI may do more harm than this small risk, and dialysis is unlikely to need any change because of the dye (ACR–NKF 2021).

Heart catheter and angiogram

Dye injected into an artery during a heart procedure carries a higher risk than a CT scan, especially when a stent is placed. The team should assess your kidney risk with a scoring tool and plan for it (KDIGO 2024, practice point 4.4.1.1).

Bowel preparations (colonoscopy)

  • Avoid sodium phosphate preparations and enemas. The FDA warns they can cause serious harm to the kidneys and heart, severe dehydration, dangerous changes in blood minerals, and death, with the highest risk in people with kidney disease or dehydration, or who take diuretics, ACE inhibitors, ARBs or NSAIDs (FDA).
  • Magnesium-based laxatives (such as magnesium citrate) can build up to dangerous levels when the kidneys fail (StatPearls). Ask which preparation is right for your kidneys.
  • On peritoneal dialysis, tell your PD unit before a colonoscopy: ISPD suggests antibiotics beforehand and draining your PD fluid so your belly is empty for the procedure (ISPD 2022).
  • On a fluid limit, ask how the large drink volume of a preparation fits with your limit.

Type 1 diabetes and fasting for a scan

  • Ask for an early-morning appointment, so you fast for less time.
  • Do not stop your basal insulin while fasting. Ask your diabetes team how to adjust it for the fasting time and for the clear-liquid day before a colonoscopy (ADA 2026 §6).
  • Bring glucose tablets or gel and tell the staff you have type 1 diabetes. Clear liquids such as apple juice or regular ginger ale count toward your carbohydrate and fluid (Treating a low).
  • CGM and MRI: take off every part of the Dexcom G7 system before an MRI. For a CT scan the sensor can stay on if it is kept out of the scanned area and covered with a lead apron (Dexcom G7 user guide). Ask about your own sensor and pump before the day.

What to do

  • Tell the doctor ordering the scan: "I have kidney disease, stage , eGFR , and type 1 diabetes. I am / am not on dialysis."
  • Ask whether the scan needs dye, and whether a drip is planned.
  • Ask which of your medicines to pause before the scan, and when to restart each one.
  • For a colonoscopy, ask for a preparation that suits kidney disease, never a sodium phosphate one.
  • Plan insulin, glucose checks and low treatment for the fasting time with your diabetes team.
  • Ask whether to remove your CGM and pump, and bring spares.
  • Ask whether you need a blood test after the scan, and when.

Examples

  • A CT at stage G4. Sara (eGFR 24, not on dialysis) needs a CT of her belly with dye. She gets saline through a drip, and her team pauses her diuretic and writes down when to restart it. A blood test her team booked for a few days later shows her creatinine is unchanged.
  • An MRI on hemodialysis. Mo needs a brain MRI with gadolinium. The radiologist uses a group II agent. He has his usual dialysis session the next day; no extra session is needed.
  • A colonoscopy. Ruth's first prescription is for a sodium phosphate preparation. She points out her kidney disease and is switched to a different preparation. Her diabetes team writes a plan for her insulin on the clear-liquid day.

Ask your care team

  1. Does this scan need dye? Is there another way to get the same answer?
  2. Will I have fluids through a drip? How does that fit with my fluid limit?
  3. Which of my medicines should I pause, and when do I restart each one?
  4. Which bowel preparation is safe for my kidneys?
  5. How should I adjust my insulin while I fast?
  6. Do I need a blood test after the scan?

Get help now if…

  • During or after a scan: trouble breathing, swelling of the face or throat, or fainting: call 911 (or your local emergency number).
  • After a bowel preparation: severe weakness, confusion, fainting, or vomiting so you cannot keep fluids down: call 911 or go to the emergency department.
  • In the days after a scan: much less urine than usual or new swelling: call your team today. See Get help now.

Sources

Not yet reviewed by a clinician. Facts and sources last checked 2026-10-06.