Renal Outcomes One Year After Metabolic Bariatric Surgery: A Clinical Audit

Introduction: Obesity increases the risk of incident chronic kidney disease (CKD), being one of the strongest risk factors for new-onset CKD even in the metabolically normal obese. Weight loss has been shown to reduce renal hyperfiltration and proteinuria. Metabolic Bariatric Surgery (MBS) remains an effective treatment for obesity and its metabolic related complications. However, literature on its impact on long term renal function remains limited. Methods: This was an observational retrospective study in a tertiary centre in Singapore. MBS cases performed at the centre between 2008 and 2019 were included. The primary outcome measure was estimated Glomerular Filtration Rate (eGFR), calculated using the CKD Epidemiology Collaboration equation, and albuminuria (defined as urine Albumin-Creatinine Ratio (uACR) >3.5 mg/mmol) at baseline and at one-year post surgery. Results: 557 patients were included. Baseline parameters are as follows: mean age 41.7 ±10.1 years; female 65.4%; ethnic composition: Chinese (35.2%), Malay (33.0%), Indian (26.9%); BMI 42.5 ±7.9 kg/m²; glycaemic status: Diabetes Mellitus (34.5%), Pre-diabetes (13.5%), Non-diabetic (52.1%); Hypertensive status: Hypertension (55.2%), Pre-Hypertension (1.9%), Normotensive (42.9%). Median eGFR was 110.9 (92.4 - 121.5) mL/min/1.73 m² and median uACR was 1.00 (0.40 - 3.55) mg/mmol. At one-year post surgery, patients achieved statistically significant reductions in mean BMI (-11.3 ±4.2 kg/m2), systolic BP (-3.24 ±19.3 mmHg), diastolic BP (-5.23 ±13.8 mmHg), fasting glucose (-1.95 ±2.89 mmol/L) and improvement in HDL (0.29 ±0.26 mmol/L). In addition, statistically significant reductions in the proportion of patients on anti-hypertensive (48.8% to 14.4%), anti-diabetic (34.1% to 12.7%) and lipid-lowering medications (37.8% to 20.4%) were seen. In particular, ACE-inhibitor and/or angiotensin receptor blocker (32.9% to 9.2%, p< 0.001) usage was reduced. At one-year post surgery, median eGFR increased by 1.66 mL/min/1.73 m² (p<0.001). Further stratification by glycemic status showed significant increases in GFR in patients without diabetes or pre-diabetes. There was a decrease in median uACR (0.30 mg/mmol, p=0.001) at one-year post surgery; this remained statistically significant in patients with diabetes and pre-diabetes. 12.9% of patients had improvements in CKD staging. The proportion of patients with albuminuria decreased from 24.8% at baseline to 1.89% one-year post surgery (p<0.001). Conclusions: Metabolic bariatric surgery had a positive impact on renal function as shown by the improvement in eGFR in the non-diabetic group, and the reduction in albuminuria in the diabetes and pre-diabetes group at one-year post surgery. More adequately powered, longer-term data is required to investigate the durability of this impact.