Natural Protection Against Contrast Agent Dangers in Imaging

Each year, millions of Americans undergo medical imaging procedures, including angiograms, CT scans and MRI. These are used with increasing frequency to examine and treat the heart, blood vessels and other internal organs and tissues. Since they’re not invasive, most people don’t think twice about undergoing these procedures… and it’s true, generally they are safe.

Yet it is important to understand that image-enhancing contrast agents (these travel through blood vessels and show up as a bright color on the CT or MRI scan to allow doctors to better visualize organs and blood vessels during the imaging process) can indeed cause problems ranging from mild to severe allergic reactions or impairment of kidney function, especially in susceptible individuals. Now researchers are looking into ways to safeguard those at risk for kidney damage… and, interestingly, one effective way may be a popular natural treatment.

CONTRAST AGENTS: 101

All contrast materials serve to improve the contrast and thus visibility of body organs and tissues in imaging tests. This enables the physician to see possible blockages, malformations or narrowings in blood vessels. Most contrast agents used for imaging are liquids containing iodine, in varying concentrations, and also of different viscosities. These can be taken orally or administered intravenously. Another contrast material, barium, is often swallowed as a drink. Barium shows up on the inside of the bowel as a bright color.

While contrast agents are helpful in identifying serious medical problems, risks associated with them include short- and long-term issues relating to hypersensitivity and how the agent gets processed by the liver and kidneys.

  • Mild to moderate kidney damage can develop in up to 25% of high-risk individuals — notably people with chronic kidney disease, diabetes or congestive heart failure — after undergoing contrast agent-enhanced imaging procedures (such as coronary angiograms).
  • Older people are at higher risk, since kidney function diminishes with age.
  • Even in people with normal kidney function, it is believed that up to 10% experience some kidney impairment, such as a temporary (not necessarily even noticeable) decrease in kidney function.
  • In severe cases, people can develop a rare but potentially fatal kidney condition known as contrast-induced nephropathy (CIN).

A SIMPLE PILL PROTECTS THE KIDNEYS

At the University of Michigan, radiologist Aine Kelly, MD, MS, and her colleagues evaluated the available body of research on how best to shield kidneys from iodinated contrast agent-induced damage. They studied the results of 41 randomized controlled trials that involved data on the protective effects of agents administered to prevent kidney damage after coronary angiograms and found that…

  • The most effective one is the inexpensive and readily accessible natural antioxidant N-Acetylcysteine (NAC). NAC is a naturally occurring derivative of a protein amino acid that, in addition to its antioxidant and kidney-protective qualities, is also being studied for benefits relative to heart disease and HIV.
  • Theophylline, a pharmaceutical drug believed to have a protective effect but also numerous side effects, did not work well. However, according to Dr. Kelly, it may have shown a benefit if there had been more data.
  • Other drugs studied were also shown to not have any significant effect, and one — furosemide — actually increased the risk for kidney damage.

These results were published in the February 19, 2008, issue of the Annals of Internal Medicine.

MORE WAYS TO LOWER RELATED KIDNEY RISKS

If you’re scheduled to have an imaging test, don’t just take for granted that the process is safe and without dangers. Dr. Kelly recommends asking your doctor about your personal health profile, including any possible risks and the best ways to lower them, in advance. Together you can decide which protective strategies make the most sense for you. Options include…

Have your kidney function tested. Many who have abnormal kidney function are unaware they have it, since it often causes no symptoms. Before undergoing an imaging test using a contrast agent, make sure that your kidney function is normal. Simple blood tests to assess kidney function include those that measure glomerular filtration rate (GFR, or how well the kidneys are removing wastes and excess fluids from the blood) and serum creatinine (a waste product) levels.

Consider taking N-Acetylcysteine (NAC). If tests find that your kidney function is diminished, or if you are at risk due to medical problems such as chronic kidney disease, diabetes or congestive heart failure, ask your doctor about taking NAC before testing. Note: Although NAC has few side effects and is widely available in health food stores, Dr. Kelly emphasizes that for this purpose, it should only be taken in prescription form under the supervision of your health care provider. Over-the-counter supplements are not recommended for pre-scan protection.

Ask your physician about using a gentler contrast agent. Even though there may be some minimal compromise to the image quality, in people at risk for kidney damage it may make sense to use a milder agent. Dr. Kelly explains that certain contrast agents are less dense, so while they might not provide equally clear images, they are less likely to impair blood flow to the kidneys.

Drink up. Confirm with your health care provider that you will be properly hydrated throughout the procedure, and even afterward, which is very important in preventing kidney impairment, notes Dr. Kelly. Continue to drink lots of fluids to help flush the agent from your body. (Caution: People with chronic kidney failure may be on a restricted fluid diet and must carefully consult with their physicians before making any changes in fluid intake.)

Before any testing, it is important to inform your doctor of all medications you take.

If you suffer from any allergies — especially if you are allergic to iodine in shellfish since many contrast agents are iodine-based — inform your physician. He/she may use a steroid preparation beforehand, order a different contrast agent or even explore alternate testing methods.

Imaging provides important information and usually the benefits outweigh the risks — though the more such tests you have, the greater likelihood they’ll have some physiological effects. If you are facing testing that involves use of a contrast agent, make sure that you and your doctor have discussed the risks versus the benefits and decided it’s necessary and worthwhile.