Xradiologist

CT Exams with Contrast

Creatinine- Don't use

Creatinine is not a good indicator of risk for contrasted exams as some studies suggest that approximately 15% of patients with normal serum creatinine levels have a GFR below 50 mL/min. Also, creatinine can be falsely elevated in those with increased muscle mass.

eGFR- > 45 mL/min.

Iodinated contrast has a risk of contrast induced nephropathy.

GFR < 40 mL/min has a risk of 4.6%
GFR > 40 mL/min has a risk of 0.6%

Thus, the safe threshold of 45 mL/min was determined.

Lab results should be from within the past 6 weeks.

Risk factors for contrast induced nephropathy-

Diabetes
Advanced age > 70 years old
History of renal insufficiency
Male gender
HIV
Solitary kidney
Dehydration
Congestive heart failure
NSAID use
Cisplatin based chemotherapy
Aminoglycoside antibiotics
Iodinated contrast within the last 72 hours

Risk reduction-

Discontinue Metformin for 48 hours after the contrasted examination to decrease the risk of lactic acidosis.

Hydration

Inpatients-
Encourage oral hydration starting the day prior to examination.
If GFR is below 60 mL/min-
IV 0.9% NS to run at 1 mL/kg for 12 hours prior to exam.

Outpatients-
Encourage oral hydration starting the day prior to examination.
If GFR is below 60 mL/min-
IV 0.9% NS bolus of 250 cc before and 250 cc after examination.

Acetylcysteine- unclear if this provides an additional risk reduction.

600 mg PO BID day before exam
600 mg PO BID day of exam
600 mg PO BID for 2 days following exam

MRI Exams with Contrast

Creatinine- Don't use

Creatinine is not a good indicator of risk for contrasted exams as some studies suggest that approximately 15% of patients with normal serum creatinine levels have a GFR below 50 mL/min. Also, creatinine can be falsely elevated in those with increased muscle mass.

eGFR- > 30 mL/min.

Gadolinium has an association with nephrogenic systemic fibrosis (NSF).

GFR < 30 mL/min has a risk of less than 4% (447 total cases reported).
GFR > 30 mL/min (Only 2 cases ever reported).

Thus, the safe threshold of 30 mL/min was determined.

The FDA no longer regards moderate renal impairment (eGFR of 30-45) as a risk.
However, the ACR suggests risk/ benefit analysis in those with eGFR of 30-45.

Lab results should be from within the past 6 weeks.

Risk factors for NSF-

Acute or chronic renal insufficiency
Liver failure
Post liver transplant
Inflammatory states
Infections
Metabolic acidosis
Elevated serum Iron, Calcium or Phosphate
Immunosuppression
Vasculopathy
High dose Erythropoietin

Gadolinium based contrast agents were classified according to their risk of causing NSF-

Group 1- Greatest number of NSF cases
Gadodiamide (Omniscan)- 283 cases reported
Gadopentetate dimeglumine (Magnevist)- 125 cases reported
98% Renal / 2% Hepatobiliary excretion (image at 60 min)
Gadoversetamide (Optimark)- 20 cases reported

Group 2- Few, if any, or unconfirmed cases of NSF
Gadobenate dimeglumine (Multihance)- 10 cases reported
Gadoteridol (Prohance)- 9 cases reported
Gadobutrol (Gadavist)

Group 3- New agents without any reported cases of NSF
Gadofosveset (Ablavar)
Gadoxetic acid (Eovist)-
50% Renal / 50% Hepatobiliary excretion theoretically decreases NSF risk. (image at 20 min)

Risk reduction-

Dialysis does not protect patients from developing NSF.