Is it safe to perform an abdominal and pelvis CT (Computed Tomography) scan with and without contrast in a patient with impaired renal function, specifically a Glomerular Filtration Rate (GFR) of 21?

CT with Contrast is Not Recommended for Patients with GFR 21

A CT scan of the abdomen and pelvis with and without contrast is not recommended for patients with a GFR of 21 due to significant risk of contrast-induced nephropathy and potential for worsening renal function. 1 Alternative imaging methods without iodinated contrast should be considered.

Risk Assessment for Patients with GFR 21

• GFR of 21 mL/min/1.73m² falls into the "high risk" category (GFR <30 mL/min/1.73m²) 1
• This level of renal impairment represents a significant contraindication to iodinated contrast administration
• The American College of Radiology identifies eGFR <30 mL/min/1.73m² as a key threshold for increased risk 1

Risks of Proceeding with Contrast CT

1. Contrast-Induced Nephropathy (CIN):

   • Patients with pre-existing renal insufficiency are at highest risk for CIN 2
   • CIN typically develops within 48-72 hours after contrast exposure 1
   • Can lead to prolonged hospitalization and increased mortality 3

2. Potential for Permanent Renal Damage:

   • May require dialysis in severe cases 3
   • Risk is significantly higher with GFR <30 mL/min/1.73m² 1

Alternative Imaging Options

1. Non-contrast CT:

   • Can still provide valuable information about:
     • Hydronephrosis
     • Renal size/volume
     • Urinary tract calculi
     • Basic anatomical information 4

2. Ultrasound:

   • Preferred screening examination for patients with decreased renal function 1
   • Can evaluate hydronephrosis and basic renal anatomy

3. MRI with macrocyclic gadolinium agents:

   • If absolutely necessary, macrocyclic gadolinium agents (Group II) can be used with caution 1
   • Lower nephrotoxicity risk compared to iodinated contrast 1
   • Still requires careful risk-benefit assessment

If Contrast Study is Absolutely Necessary

If the diagnostic information is essential and not available with non-contrast imaging:

1. Risk Mitigation Strategies:

   • Implement aggressive hydration protocols (IV isotonic saline at 1 mL/kg/hr for 6 hours before and 6-12 hours after) 1
   • Use lowest possible diagnostic dose of contrast 1
   • Temporarily discontinue nephrotoxic medications (NSAIDs, aminoglycosides) 1
   • Consider hemodialysis after the procedure (though effectiveness is uncertain) 5

2. Contrast Selection:

   • Use low-osmolar or iso-osmolar contrast agents 1
   • Absolute minimum dose necessary for diagnosis 1

Important Caveats

• The decision to use contrast should be based on urgency and importance of diagnostic information 1
• The harms of delaying diagnosis must be weighed against risk of worsening renal function
• Patients should be monitored for signs of CIN with follow-up renal function testing within 48-72 hours 1
• Metformin should be withheld for 48 hours after contrast administration if it is used 1

In conclusion, for a patient with GFR 21, a non-contrast CT or alternative imaging modality should be strongly considered instead of CT with contrast due to the significant risk of further kidney damage.