Determinants of glomerular filtration rate following bariatric surgery in individuals with severe, otherwise uncomplicated, obesity: an observational, prospective study.

Aims: Obesity-induced nephropathy is an established clinical entity arising from a "maladaptive" response to lipid accumulation at the nephron level. Bariatric surgery positively affects renal function, reducing or increasing glomerular filtration rate (GFR) in subjects with hyperfiltration and renal impairment, respectively. The effect of this surgery in patients with normal estimated GFR (eGFR) is less clear.

Methods: A complete clinical and biochemical assessment of 135 severely obese, otherwise healthy subjects, was obtained before Roux-en-Y gastric bypass (RYGB). All subjects underwent an OGTT with plasma glucose and insulin determinations. Follow-up data were recorded at 6, 12, 24 and 48 months after intervention.

Results: Baseline eGFR was 98.2 ± 13.6 ml/min/1.73 m; hyperfiltration (>120 ml/min/1.73 m) was present in 7% of the cohort. No eGFR variation over the follow-up emerged, except at the last visit (-3.6 ± 1.4 ml/min/1.73 m at month 48, p = 0.01 vs baseline). In the univariate analysis, the renal performance at 48 months was inversely related to baseline eGFR (r = -0.17, p = 0.04) and plasma triglycerides (r = -0.04, p = 0.05). Fasting and OGTT-derived variables did not impact eGFR. By multiple regression analysis, eGFR time course was independently predicted only by baseline eGFR (p = 0.03). Interestingly, patients having a baseline eGFR >100 ml/min/1.73 m (median value) showed, after 48 months, an average loss of -8.3 ± 2.2 ml/min/1.73 m, while those with eGFR <100 exhibited a slight increase (+1.8 ± 2.3 ml/min/1.73 m, p < 0.01).

Conclusions: Long-term data confirm the safety of RYGB on renal function. Interestingly, a subtle hyperfiltration, i.e., occurring in high-normal range of eGFR, is attenuated by surgical procedure. Lastly, high serum triglycerides may track an unfavorable renal outcome.