The study also did not assess potential ways to protect against kidney damage from gadolinium contrast agents used in MRI (magnetic resonance imaging) scans. Since May 2007, those contrast agents have carried a warning from the U.S. Food and Drug Administration about risk to kidneys.

Kelly, Carlos and their colleagues performed the study to try to get a firm answer to a question that has puzzle medical imaging specialists for years.


Although many drugs have been tried for prevention of iodine-related contrast-induced nephropathy, contradictory evidence has emerged from studies of how well they work. The result has been widespread variation in what hospitals and medical imaging centers do before scanning a patient.

Although a prospective trial comparing N-acetylcysteine directly to other drugs should be conducted to verify the U-M team's findings, the team hopes its new study will help guide both clinicians and patients.

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.

And, since most kidney problems cause no symptoms, even healthy people might want to ask their doctors to test their blood creatinine levels before sending them for a scan.

Creatinine levels go up when the kidneys aren't operating efficiently. Contrast-induced nephropathy is defined as a 25 percent or greater increase in creatinine within 48 hours of receiving contrast agent. The new study evaluated the impact of pre-scan medicines by looking at their impact on patients' creatinine levels, as a surrogate for kidney function.

The problem of contrast-induced nephropathy is a relatively recent one - a byproduct of the dramatic increase in the use of CT scans and X-ray guided procedures such as angioplasty.

The benefit of these scans is not in question: Intense X-rays can reveal valuable information about injuries, diseases, and patients' response to treatment. Iodine-containing agents allow doctors to improve the scans even further, giving better "contrast" between the blood vessels and tissue, because X-rays are scattered differently by iodine. But as the iodine is carried by the blood to the kidneys, and filtered out into the urine, the iodine can upset the delicate balance that keeps the kidneys functioning.

In recent years, manufacturers of contrast agents have begun to offer different formulations that may pose less risk to patients' kidneys. More expensive low-iodine and iodine-free agents are available to especially vulnerable patients, and to people who are allergic to iodine. But for everyone else, medical imaging specialists have tried to find ways to prevent the damage.

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