Despite multiple studies assessing post-nephrectomy kidney function, data and validated tools for predicting postoperative kidney function are lacking. “Clinically significant consequences of chronic kidney disease (CKD) after nephrectomy are not common; however, there is an association between lower kidney function and mortality in patients after nephrectomy,” explains Robert J. Ellis, MD, PhD. “Therefore, it’s important to identify patients who are at increased risk for these adverse outcomes, even if this risk is marginal, to potentially develop strategies for minimizing risk.”

Developing a Screening Tool

For a study published in the Journal of the American Society of Nephrology, Dr. Ellis and colleagues conducted a study to develop a screening tool to identify patients scheduled for nephrectomy for kidney cancer who are at higher risk of developing clinically significant CKD within the first 12 months, as well as those who have a low risk for this outcome. The researchers used an existing population-based cohort to collect data and assess patterns of care for kidney cancer. After initial development, the team applied the tool to four different populations of patients undergoing nephrectomy, to assess external validity.

The team developed a clinical scoring tool based on a limited multivariable model. Variables included in developing the tool and scores included age, preoperative kidney function, diabetes status, and chosen treatment. Level of risk was divided into four groups based on predicted likelihood of a 12 months postoperative eGFR of less than45 ml/min per 1.73 m2, chosen based on large observational studies indicating an association with increased mortality risk and continued eGFR decline. The four defined groups were negligible (0-3 points; 0.8% likelihood), low (4-6 points; 6% likelihood), moderate (7-8 points; 23% likelihood), and high (9-10 points; 51% likelihood). “Candidates for nephrectomy can be grouped into these four groups, based on patient factors and whether partial or radical nephrectomy is the intended management strategy,” explains Dr. Ellis (Figure). Within the derivation and validation cohorts, absolute risks of stage 3b or higher CKD were less than 2%, 3%-14%, 21%-26%, and 46%-69% across the negligible-, low-, moderate-, and high-risk groups, respectively. The negative predictive value of the negligible risk category was 98.9% for clinically significant CKD. The c statistic for the clinical score model was between 0.84 and 0.88 across derivation and validation cohorts.

“The tool was validated by several independent centers and continued to have encouraging predictive value in populations outside the derivation cohort (c statistics were consistently ≥0.84),” emphasizes Dr. Ellis.

Next Steps

“This tool was designed to include only variables that should be available in an outpatient setting, and scores should be easy to calculate,” notes Dr. Ellis. “Decisions regarding surgical management of kidney cancer are complex and involve assessment of patient, tumor, and hospital factors. This score is intended to provide a standardized way to evaluate risk of developing clinically important CKD after nephrectomy, and act as a simplified piece of the relatively complex puzzle that needs to be put together when making preoperative decisions.”

When considering improving and enhancing the tool, Dr. Ellis believes it would benefit from studying longitudinal exploration of CKD risk. “Extending follow up to 5 or 10 years, and assessing clinically significant CKD, kidney failure, or mortality as outcomes would greatly improve the clinical applicability of this score,” he explains.