#4706 THERAPEUTIC AND PROGNOSTIC IMPACT OF KIDNEY BIOPSY FINDINGS IN PATIENTS AGED 80 YEARS AND OLDER: A MULTICENTER RETROSPECTIVE COHORT STUDY (KB-OLD)
Authors: Hamroun Aghiles , Lenain Rémi , Nicolazzi Paul , Gomis Sébastien , Maanaoui Mehdi , Gibier Jean-Baptiste , Glowacki Francois 
Published: June 2023

Abstract

Background and Aims
The great phenotypic heterogeneity in the presentation of kidney diseases makes the diagnostic strategy all the more complex in the elderly. While kidney biopsy should play a pivotal role, its non-negligible risk of bleeding complications (2-5% in the general population) justifies a certain reluctance to its application in the elderly. To date, however, there is little data on the benefit-risk ratio of kidney biopsy in the elderly. Most of these studies have focused on a relatively young population (60-70 years old) and on a limited number of patients. Concerning patients aged 80 years and older, very few studies have described the real therapeutic influence of kidney biopsy findings with regard to the rate of complications. Moreover, none of these studies have evaluated the long-term prognostic impact of therapeutic changes induced by the results of the kidney biopsy. The main objectives of this study are to describe the indications, diagnoses, complication rate, therapeutic influence and the prognostic impact of a change in therapeutic management after native kidney biopsies performed in patients aged 80 years and older.

Method
The KB-Old study (Kidney Biopsy for Old) is a retrospective multicenter cohort that consecutively included all patients aged 80 years and older who underwent percutaneous native kidney biopsy in 17 centers in the northern region of France, between 2010 and 2020. Clinical, biological and anatomopathological data as well as post-biopsy follow-up (therapeutic strategy, occurrence of complications) were collected from medical records. All pathology examinations were analyzed centrally by a team of experienced nephropathologists. Events of death or kidney failure were identified by specific registry cross-linking. To analyze the prognostic impact of therapeutic management following kidney biopsy (either initiation of a specific treatment or simple nephroprotection) on the risk of kidney failure and death, we performed Cox models weighted by propensity score (Inverse Probability of Treatment Weighting -IPTW-) in the population potentially eligible for treatment (exclusion of diseases without specific treatment). The areas under Kaplan Meier curves were calculated up to 6 years of follow-up (Restricted Mean Survival Time - RMST) and compared according to the initiation of a specific treatment after the kidney biopsy. This study was approved by Institutional Review Board (#AUG-20-707).

Results
Overall, the cohort included 453 patients (54% men, median age 83 years), half of whom underwent biopsy in the context of acute kidney injury (median serum creatinine level 3.0 mg/dl). The main diagnoses were nephroangiosclerosis (15%), renal involvement of hematological malignancies (13%), acute tubulointerstitial nephritis (12%) and vasculitis (10%). The complication rate was approximately 10%, with only 2.8% of serious complications requiring therapeutic intervention (mostly transfusion). The kidney biopsy identified a disease potentially accessible to a specific treatment in 73% of cases. After exclusion of patients with ineligible diseases, a specific treatment was initiated in about one out of two cases (163/332, 49%). After weighting on propensity score, the two treatment groups were globally balanced. A beneficial effect of treatment on dialysis-free survival was observed (HR = 0.51 [0.28-0.92], p = 0.02), without any major influence on mortality (Figure 1). Over a 6-year follow-up period, there was a gain in dialysis-free survival in the treated group estimated by the delta RMST at +10.46 months [3.39 - 17.54] compared with the untreated group (p = 0.004), with no difference in overall life expectancy.

Conclusion
To the best of our knowledge, this is the largest multicenter cohort of patients aged 80 years and over who have undergone kidney biopsy. It seems to confirm the interest and safety of this examination for specific indications, and a potentially important benefit on the prognosis when it leads to an adapted therapeutic management.