Longitudinal assessment of renal function in native kidney following bariatric surgery

The epidemic of obesity parallels that of chronic kidney disease (CKD). Obesity worsens the course of CKD mainly defined by an abnormal glomerular filtration rate (GFR). Patients with severe obesity stages (II and III with body mass index, BMI >35 kg/m2) are eligible for bariatric surgery (BS), which is the most efficient method of achieving durable weight loss. BS may reverse glomerular hyperfiltration, albuminuria, improve adipocytokine profile, and relieve diabetes and hypertension. Obesity remission following BS might prevent the progression of renal failure in populations with morbid obesity. However, evidence for the beneficial effect of BS on renal function is scanty. This lack of knowledge is mainly due to methodological reasons, which are addressed in this review. The reversibility of hyperfiltration due to the presence of functional renal reserve hampers the interpretation of changes in true GFR after BS. This true GFR is only obtained with the renal clearance of an exogenous filtration marker. Estimation of GFR is generally provided by prediction equations, namely by MDRD (Modification of Diet in Renal Diseases) or by CKD-EPI (Chronic Kidney Disease – Epidemiology collaborative group). These equations are not accurate because the serum levels of both creatinine and cystatin C depend on extra-renal factors, which are modified by BS. Comparing the slopes of measured GFR according to various durations of exposure to morbid obesity would be critical in providing reliable data. Herein, we review the current knowledge on the effects of BS on kidney function, we specify the methodological issues and particularities of the dietary management of CKD patients in order to propose reliable directions for future clinical research