Iodine-based contrast material that is injected intravenously to enhance CT images is safe to use in most patients, according to a new study published online in the journal Radiology. This goes against the case reports published in the 1950s, 1980s and 1990s asserting that iodine-based contrast is associated with kidney damage or contrast-induced nephropathy (CIN).

"Existing dogma suggests that kidney injury from contrast leads to a greater risk of dialysis or mortality - these adverse outcomes are the main reason why contrast is withheld from patients with suboptimal renal function," Dr. Robert McDonald, radiology resident at Mayo Clinic, wrote in an email to DOTmed News. Performing some CT exams without contrast is often done at the expense of diagnostic accuracy, he added.

The case reports from the 1950s were not controlled and included one or more cases of renal function getting worse a few days after a patient was given iodine-based contrast. The studies in the 1980s and 1990s were also uncontrolled.

"We think these data and the reasoning behind these data are fundamentally flawed," wrote McDonald. "From an evidence-based medicine perspective, these data should have never been used to guide clinical practice, but this was the only data available at the time."

McDonald and his team of researchers evaluated information on patients who underwent abdominal, pelvic and thoracic CT scan at the Mayo Clinic from 2000 to 2010. The study group comprised 21,346 patients — 10,673 who underwent a CT exam with contrast and 10,673 who underwent the exam without the contrast.

The groups were matched based on gender, race and pre-existing conditions such as diabetes, congestive heart failure and acute renal disease. The researchers then investigated whether any adverse events occurring after the scans included acute kidney injury, emergency renal dialysis and death within 30 days of being exposed to contrast.

They found that there was no significant difference in the rate of acute kidney injury between the group that received contrast — 4.8 percent — and the group that didn't receive contrast — 5.1 percent. Additionally, the rates of emergency dialysis and death were also not significantly different between the two groups.

The researchers also found the same results for patients with conditions that are thought to predispose a patient to kidney injury including compromised kidney function, congestive heart failure and diabetes.

McDonald and his team conducted research in April and found similar results, so the results of this study weren't much of a surprise to him, but may be a surprise to those who have accepted those previous studies of decades ago as fact. "We are very excited about these results as they could help change clinical practice."

The previous research they conducted already spurred the hospital to use contrast in patients with impaired renal function. However, they don't give contrast to all of their patients. McDonald said that they give 95 percent of the patients contrast but not the other 5 percent, since they have the most severe form of kidney injury.

"We are still judicious in the use of contrast in this group of patients who are potentially at highest risk for CIN," said McDonald. "In these patients, we administer contrast only after discussion with the ordering physician, when the use of contrast is deemed to be beneficial or when the risk of missing a diagnosis outweighs the potential risk of an adverse event."

He thinks the findings are a "reasonable first step" but that it's not definitive proof that CIN does not exist at all. But what they did find is that if it does exist, then it's extremely uncommon.

Going forward, he thinks that the worry concerning the phenomenon will fade, but that it will take time. "This has been medical dogma for 60 years and we expect it will take years to 'convince' the medical community," he said. "In order to accomplish this, these results need to be disseminated."