Dyes containing iodine used to enhance CT scan quality can seriously harm kidneys; and a new study recommends that patients take an inexpensive pre-scan drug, called N-acetylcysteine which protects kidneys from damage. These ‘dyes’ or contrast agents put many older people and those with diabetes or heart failure at the most risk, and they have the most to gain from taking the drug.
The study is published in the Annals of Internal Medicine by researchers from the University of Michigan Health System, who were led by Aine Kelly, M.D., M.S., an assistant professor in the Department of Radiology at the U-M Medical School. The study is a meta-analysis of data from 41 randomized controlled studies that evaluated various drugs for their ability to protect kidneys: only N-acetylcysteine prevented contrast-induced nephropathy. Theophylline was not as effective, while furosemide actually raised kidney risk.
"Our goal is to improve the safety and quality of these common tests by studying drugs that reduce the risk of kidney failure," says senior author Ruth Carlos, M.D., associate professor of radiology.
Mild to moderate kidney damage occurs in one in four high-risk people who have CT scans, and in as many as one in ten people with normal kidney function. In some cases, it causes acute kidney failure. "Millions of people receive contrast agent each year, including most heart patients who have angioplasties and stents, as well as those having a CT scan. Contrast agent helps physicians see the things we need to see, but it also does pose a hazard to some people," says Kelly. "This drug, which is quick, convenient, inexpensive and widely available, with no major side effects, appears to be the best choice to protect those whose kidneys are most at risk."
In fact, Kelly says, patients who know they have weakened kidneys – also called impaired renal function – should speak up when their doctor orders a CT scan, angiogram or angioplasty, and make sure they get a tablet of N-acetylcysteine beforehand.
Source: Annals of Internal Medicine, 19 February 2008, Volume 148 Issue 4