Early Changes in Renal Function and Hemodynamics of Obese Patients after Bariatric Surgery

BACKGROUND: Weight loss 1 to 2 years after bariatric surgery (BS) improves renal hemodynamics in obese individuals, but the renal hemodynamic effect as early as 3 to 4 months after BS is unknown. We investigated the changes in glomerular filtration rate (GFR), renal plasma flow (RPF), and GFR estimates (eGFR) at 3 to 4 months after BS.METHODS: Ten patients with BMI ≥ 35 kg/m2, serum Cr ≤ 1.4 mg/dL, and undergoing BS at E-DA hospital were enrolled. Participants were asked to receive technetium 99-diethylenetriamine pentacetic acid (99Tm-DTPA) renal scans for GFR and technetium 99-mercaptoacetyl triglycine (99Tm-MAG3) renal scans for RPF both prior to and 3 to 4 months post-BS. Serum creatinine (Cr), cystatin C (Cys C), aldosterone, and renin levels were also checked before and after BS.RESULTS: After BS, four participants received renal scans for GFR while six received renal scans for RPF. Despite a significant weight reduction at 3 to 4 months after BS, changes in GFR (170.00 ± 70.78 to 125.18 ± 29.65 mL/min, P = 0.140) and RPF (350.00 ± 68.66 to 315.42 ± 57.39 mL/min, P = 0.232) did not reach a statistically significant level. However, there was a significant increase in the ratio of aldosterone to renin after BS (12.32 ± 13.47 to 34.94 ± 29.99, P = 0.043). While eGFR correlated strongly with measured GFR prior to BS, the correlation was poor at 3 to 4 months post-BS. When comparing pre-BS eGFR with measured GFR indexed for body surface area, incorporating Cr into a formula yielded a better estimation than using a formula with Cys C alone.CONCLUSION: Weight loss in the early phase of post-BS is insufficient to improve renal hemodynamics in obese individuals. The eGFR correlates well with measured GFR before BS, but the correlation is poor at the early phase after BS.