#1382 Kidney outcomes after bariatric surgery: a population-based cohort study
Authors: Sørensen Christian Goul , Jespersen Bente , Christiansen Christian Fynbo , Jensen Simon Kok , Thomsen Reimar , Gribsholt Sigrid Bjerge 
Published: May 2024

Abstract

Background and Aims
Obesity is associated with nephrolithiasis, chronic kidney disease (CKD), and kidney failure. Bariatric surgeries, including Roux en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), are effective treatments of severe obesity and may mitigate obesity-related kidney diseases such as CKD and kidney failure, but could on the other hand induce hyperoxaluria and nephrolithiasis, posing a potential risk to the kidneys.
We examined the risk of nephrolithiasis, acute kidney injury (AKI), CKD, and kidney failure after bariatric surgery.

Method
We included individuals undergoing bariatric surgery (RYGB or SG) in Denmark between 2006 and 2018 using population-based registries. These individuals were age- and sex-matched 1:5 to a background general population cohort and a cohort with hospital-diagnosed obesity. Nephrolithiasis was identified by diagnosis codes within the Danish National Patient Registry (DNPR). AKI was defined as an increase in serum creatinine (sCr) of ≥26.5 µmol/L within 48 hours or a relative increase of ≥1.5 times within seven days or from a median outpatient baseline value. CKD was defined as the presence of two outpatient eGFR samples below 60 ml/min/1.73 m2, with a minimum interval of three months between each measurement. Kidney failure was defined by recordings of kidney transplantation or chronic dialysis in DNPR.
One- and ten-year cumulative incidences (risks) were computed for each cohort accounting for the competing risk of death. Rates of incident nephrolithiasis, AKI, incident CKD, and incident kidney failure in post-bariatric-surgery patients were compared with the background population cohort and obesity cohort using multivariable Cox regression adjusting for age, sex, and Charlson Comorbidity Index (CCI)-score.

Results
We included 18,827 individuals with bariatric surgery (17,200 with RYGB and 1,627 with SG). Median follow-up was 8.1 years (5.2-9.2), 8.0 years (4.6-9.1), and 7.9 years (4.2-9.1) for the overall bariatric cohort, the background population cohort, and the obesity cohort, respectively.
Within the bariatric cohort, the ten-year risk of nephrolithiasis was 2.8%, the one-year risk of AKI was 2.7%, while the ten-year risks of CKD, and kidney failure were 0.2% and 0.1%, respectively. When comparing the post-bariatric-surgery cohort with the general population cohort, the adjusted hazard ratio (HR) was 2.92 (95% CI; 2.61, 3.27) for nephrolithiasis, 2.60 (95% CI; 2.06, 3.28) for AKI, 0.36 (95% CI; 0.18, 0.73) for CKD, and 0.81 (95% CI; 0.49, 1.32) for kidney failure. Compared with the obesity cohort, the adjusted HRs for adverse events were at 1.73 (95% CI: 1.56, 1.91) for nephrolithiasis, 1.63 (95% CI; 1.38, 1.92) for AKI, 0.41 (95% CI; 0.26, 0.66) for CKD, and 0.65 (95% CI; 0.42, 0.98) for kidney failure.

Conclusion
Individuals with bariatric surgery had a higher ten-year rate of nephrolithiasis and a higher one-year rate of AKI, but reduced rates of CKD and kidney failure within ten years after surgery compared with both the background cohort and the obesity cohort.