There is no evidence that intra-arterial administration of iodine-based contrast media is more toxic to the kidneys than intravenous injections, according to Swedish researchers. In fact, there is indirect evidence that may point to intravenous injections being more nephrotoxic than intra-arterial because the injected dose rate is usually higher, they added.
Consensus panels, recent editorials, and the 2011 updated European Society of Urogenital Radiology (ESUR) Contrast Media Safety Committee guidelines state that intra-arterial (IA) administration of iodine contrast media appears to pose a greater risk for contrast-induced nephropathy (CIN) than intravenous (IV) administration.
This position is being disputed by Dr. Ulf Nyman and colleagues from the department of diagnostic radiology at the University of Lund, Lasarettet Trelleborg, Sweden, in a recently published article in European Radiology (3 February 2012). They believe that an emphasis on IV contrast administration could be jeopardizing patient safety by inadvertently leading to higher contrast use.
For example, radiologists might end up using more IV contrast in patients with higher background risk factors in the belief that it would be safer than IA administration (Radiology, June 2007, Vol. 243:3, pp. 622-628). Also, the risk threshold for CIN is higher for IA administration than it is for IV administration: an estimated glomerular filtration rate (GFR) of less than 60 mL/min/1.73 m2 for IA contrast, compared with less than 45 mL/min/1.73 m2 for IV contrast (Eur Radiol, December 2011, Vol. 21:12, pp. 2527-2541).
"We fear that these suggestions may jeopardize patient safety by hinting at the use of higher IV contrast media doses in azotemic patients without reference to any studies comparing the risk of CIN following IV and IA injections in cohorts with matched contrast media doses and risk factors," the researchers wrote.
Nyman and colleagues also note that a bias selection of patients with fewer risk factors may explain the seemingly lower rate of CIN after CT in comparison with coronary interventions.
- In IA coronary procedures and most other IA angiographic examinations, contrast media injections are also intravenous relative to the kidneys.
- The rate of CIN following IA coronary procedures may also be exaggerated owing to other causes of acute kidney failure, such as hemodynamic instability and microembolization.
- Roughly the same gram-iodine/GFR ratio (approximately 1:1) as a limit of relatively safe contrast media doses has preliminarily been found for both IV CT and IA coronary procedures.
- The substantially higher injected IV contrast media dose rate during CT relative to an IA coronary procedure might actually pose a higher risk of CIN following CT.
"Why should the same amount of contrast media injected IA be more nephrotoxic than if injected IV in the same patient when the vast majority of IA injections are IV relative to the kidneys with the exception of suprarenal aortic and selective renal injections?" Nyman said in an interview with AuntMinnieEurope.com.
It's important for radiologists to know this information because they may underestimate the risk of CIN in high-risk patients undergoing contrast-enhanced CT if they think IA administration of contrast is more toxic, he said.
The definitive answer will come only through more research. Studies are needed to compare the CIN risk in patients undergoing IA and IV examination with matched risk factors and contrast medium doses, Nyman added.
