Medicare patients who live in areas of the country with high rates of abdominal and chest CT exams face a higher risk of undergoing nephrectomy, researchers found.
That correlation between CT scanning and nephrectomy is even stronger in larger hospital regions with more than 50,000 Medicare patients, Gilbert Welch, MD, MPH, of Dartmouth University and colleagues reported online in JAMA Internal Medicine.
The team focused on nephrectomy because it’s commonly performed for kidney cancer, which is frequently diagnosed as an incidental finding on an abdominal or chest CT. In addition, there’s a “growing recognition that not all kidney cancers have the same potential for insidious progression and metastasis,” they noted.
For the study, Welch and colleagues assessed Medicare claims from more than 15 million patients to measure five-year risk of imaging and nephrectomy within each of 306 hospital referral regions (HRRs) in the U.S. During that time, 43% of Medicare beneficiaries had either a chest or abdominal CT, with the geographical risk ranging from 31% in Santa Cruz, California, to 52% in Sun City, Arizona.
They found that an increased regional CT risk was associated with a higher risk of nephrectomy (r=0.38, 95% CI 0.28-0.47), with an even greater association among HRRs with more than 50,000 Medicare beneficiaries (r=0.47, 95% CI 0.31-0.61).
After controlling for adult smoking rates within HRRs, imaging an additional 1,000 beneficiaries was associated with four additional nephrectomies, and the case-fatality rates for nephrectomy were 2.1% at 30 days and 4.3% at 90 days.
The ability to make causal inferences based on the results of the study was limited by its observational nature: “While claims data are a reliable data source for use of medical care … they are less reliable indicators of the reason services are being used,” the researchers autioned. “Thus, we cannot make any judgments about the appropriateness of imaging.”
As for the policy implications of their study, Welch and colleagues pointed to the increasing role of active surveillance in managing small renal masses, particularly for elderly patients. For example, a study presented at the most recent Genitourinary Cancers Symposium reported that a growing number of patients with small renal masses are opting for active surveillance over immediate treatment.
“We believe surgeons should routinely offer active surveillance for small renal masses, and that patients, after being informed about the small risk of developing metastatic disease, should give the option serious consideration,” they wrote.
Welch and colleagues also pointed out that the decision to conduct an imaging test as part of active surveillance should take into account both its potential benefits and harms. And while the radiation risk associated with CT is perhaps the most well known potential harm, they wrote that their findings “suggest that the risk of nephrectomy is more than an order of magnitude higher.”
In a commentary accompanying the study, Rebecca Smith-Bindman, MD, of the University of California San Francisco, wrote that the study by Welch and his colleagues “adds renal to breast, lung, prostate, and thyroid cancers as cancers with increased morbidity from incidental findings or overdiagnosis.”
She argued that the results of the study reinforce the need for clinical decision support tools that consider overdiagnosis as harm, as well as the development of consistent standards on how to perform and interpret CT scans.
A larger discussion about how aggressively to follow incidental findings — particularly if treatment is unlikely to affect survival — is also needed, Smith-Bindman wrote. “But that is easier said than done. Once a suspected cancer is found, it is nearly impossible to ignore. The suspected diagnosis opens a Pandora’s box, so the only way to decrease overdiagnosis is to avoid unneeded tests in the first place.”
The study was partially supported by the National Institute on Aging.
A co-author reported being an investor in Dorsata Inc., a software company that implements clinical pathways.