A Simple Clinical Tool for Stratifying Risk of Clinically Significant CKD after Nephrectomy: Development and Multinational Validation
Authors: Ellis Robert J. , Del Vecchio Sharon J. , Gallagher Kevin M.J. , Aliano Danielle N. , Barber Neil , Bolton Damien M. , Chew Etienne T.S. , Coombes Jeff S. , Coory Michael D. , Davis Ian D. , Donaldson James F. , Francis Ross S. , Giles Graham G. , Gobe Glenda C. , Hawley Carmel M. , Johnson David W. , Laird Alexander , Leung Steve , Malki Manar , Marco David J.T. , McNeill Alan S. , Neale Rachel E. , Ng Keng L. , Phipps Simon , Stewart Grant D. , White Victoria M. , Wood Simon T. , Jordan Susan J. 
Published: April 2020

Significance Statement
Patients undergoing surgical management of kidney tumors are at increased risk of developing CKD. However, it is often difficult to identify patients at higher risk of clinically significant CKD before surgery, and there is a lack of validated tools to assist clinicians in this process. The authors developed and validated a simple scoring system that accurately and reproducibly stratifies risk of developing clinically significant CKD after nephrectomy on the basis of readily available parameters. This system provides an evidence-based quantitative tool for clinicians to balance the risk of CKD against other considerations when planning management of kidney tumors, and it will facilitate earlier identification of patients with a higher risk of developing clinically significant CKD, potentially leading to earlier intervention.

Background
Clinically significant CKD following surgery for kidney cancer is associated with increased morbidity and mortality, but identifying patients at increased CKD risk remains difficult. Simple methods to stratify risk of clinically significant CKD after nephrectomy are needed.

Methods
To develop a tool for stratifying patients’ risk of CKD arising after surgery for kidney cancer, we tested models in a population-based cohort of 699 patients with kidney cancer in Queensland, Australia (2012–2013). We validated these models in a population-based cohort of 423 patients from Victoria, Australia, and in patient cohorts from single centers in Queensland, Scotland, and England. Eligible patients had two functioning kidneys and a preoperative eGFR ≥60 ml/min per 1.73 m2. The main outcome was incident eGFR <45 ml/min per 1.73 m2 at 12 months postnephrectomy. We used prespecified predictors—age ≥65 years old, diabetes mellitus, preoperative eGFR, and nephrectomy type (partial/radical)—to fit logistic regression models and grouped patients according to degree of risk of clinically significant CKD (negligible, low, moderate, or high risk).

Results
Absolute risks of stage 3b or higher CKD were <2%, 3% to 14%, 21% to 26%, and 46% to 69% across the four strata of negligible, low, moderate, and high risk, respectively. The negative predictive value of the negligible risk category was 98.9% for clinically significant CKD. The c statistic for this score ranged from 0.84 to 0.88 across derivation and validation cohorts.

Conclusions
Our simple scoring system can reproducibly stratify postnephrectomy CKD risk on the basis of readily available parameters. This clinical tool’s quantitative assessment of CKD risk may be weighed against other considerations when planning management of kidney tumors and help inform shared decision making between clinicians and patients.