Association of Kidney Length with Clinical Outcomes among Individuals with CKD

Background: The assessment of kidney health is typically limited to estimates of glomerular filtration (eGFR) and glomerular integrity (albuminuria). These are insufficient, given the complexity and heterogeneity of renal pathology, and disease misclassification using these biomarkers is a well-known problem in clinical and research settings. Measuring and evaluating kidney size may provide a complementary understanding of kidney function and structure, particularly among individuals with chronic kidney disease (CKD). Methods: We studied 3,585 non-dialysis requiring CKD patients from Vanderbilt University Medical Center’s electronic health record (EHR) databank, BioVU. We ascertained kidney length using computational free text mining techniques within abdominal MRI radiology report notes. We examined associations of kidney length with time to end-stage kidney disease or death, using Cox proportional hazards regression models stratified by diabetes status. Secondarily, a phenome-wide association study was conducted to explore associations of kidney length with other phenotypes in the EHR. Results: During a median follow-up of 2.5 years, 138 patients had an incident ESKD event and 643 died (incidence rate for composite endpoint: 6.0 events per 100 person-years). After adjustment, among non-diabetic patients (n=2,515), shorter kidneys were associated with risk of the combined endpoint (hazard ratio (HR), 1.08 (1.02, 1.15) for each cm increment in kidney length, p=0.012). In contrast, kidney length was not associated with risk of ESKD or death among diabetic patients (HR 1.04 (0.92, 1.18)). PheWAS signaled additional associations of kidney length with subclinical and clinical cardiovascular outcomes, acute kidney injury and liver diseases. Conclusion: Shorter kidney length was associated with an increased risk of ESKD and mortality among CKD patients without diabetes. Efforts to establish the broader clinical significance of kidney size are underway.