Why GFR matters in MRI, GFR Guidelines for MRI contrast

Why GFR matters in MRI

• In MRI, gadolinium-based contrast agents (GBCA) are sometimes injected to enhance images.

• If a patient’s kidneys are not working well (low GFR), the body can’t clear gadolinium quickly.

• In severe kidney failure, gadolinium can rarely cause a dangerous condition called Nephrogenic Systemic Fibrosis (NSF) — thickening and hardening of the skin and other tissues.

GFR Guidelines for MRI contrast

eGFR (mL/min/1.73m²)	MRI Contrast Use Recommendation
≥ 60	Safe to give GBCA
30–59	Usually safe, but use lowest dose, avoid in high-risk patients
< 30	Avoid GBCA unless absolutely essential (use safer macrocyclic agents if needed)
Dialysis patient	GBCA only if necessary, and schedule dialysis immediately after

Typical hospital protocol before MRI with contrast

1. Check serum creatinine within last 1 month (or last 7 days for high-risk patients).

2. Calculate eGFR.

3. If GFR is low, discuss with the referring doctor whether contrast is necessary.

4. If contrast is given to a patient with impaired kidney function, use safer GBCA types (macrocyclic, non-ionic) and minimal dose.

GFR (Glomerular Filtration Rate)
GFR is a measure of how well your kidneys are filtering blood. Specifically, it estimates the volume of fluid filtered by the glomeruli (tiny filters in the kidneys) each minute.

Why it’s important

• It’s the main indicator of kidney function.

• Used to detect, stage, and monitor Chronic Kidney Disease (CKD).

• Helps guide treatment decisions, especially for kidney-related illnesses and drug dosing.

Normal & abnormal values

GFR (mL/min/1.73m²)	Kidney Function
≥ 90	Normal
60–89	Mildly decreased
45–59	Mild to moderately decreased
30–44	Moderately to severely decreased
15–29	Severely decreased
< 15	Kidney failure (end-stage)

How GFR is measured

1. Estimated GFR (eGFR) – Calculated from blood creatinine, age, sex, and sometimes race.

2. Measured GFR (mGFR) – More accurate, uses special markers (like inulin, iohexol) in research or special cases.

Factors affecting GFR

• Lower GFR: CKD, acute kidney injury, dehydration, heart failure.

• Higher GFR: Early diabetic nephropathy, pregnancy.

• Temporary changes: High-protein meal, exercise.