Written by Jasna Trbojevic-Stankovic
Reviewed by Anna Solini
Impact of bariatric surgery on renal outcomes
Bariatric surgery (BS) in obese patients with preserved kidney function lowers the risks of estimated glomerular filtration rate (eGFR) decline, of doubling of serum creatinine and of end-stage renal disease . Since there are changes in plasma creatinine (pCr) after large weight loss, pCr-based eGFR calculating formulas, Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), tend to overestimate the correction of eGFR with regard to true measurement. Although CKD-EPI may be the best performance formula for measuring eGFR in morbidly obese , cystatin C-based eGFR (eGFRcys) would be better equation if adjusted for body surface area . BS can reduce albuminuria in patients with severe obesity and normal kidney function by reducing systemic inflammation, as high-sensitivity C-reactive protein was found as an independent risk factor for albumin to creatinine ratio (ACR) .
One study found that the main factors that are able to predict the variation in eGFR of obese individuals are baseline eGFR and, particularly, triglycerides after surgery, when adjusted for multiple variables . Another study in nondiabetic individuals with severe obesity identified certain clinical and vascular predictors of GFR improvement. Among vascular parameters, a normal renal resistive index and the absence of extensive vascular remodeling (as indicated by smaller brachial artery diameter and lower carotid intima media thickness) are associated with a greater increase in GFR one year after bariatric surgery. In this study, an increase in GFR after the surgery was significant only upon adjustment for body surface area and not when expressed in absolute values . In addition, BS is an effective procedure in achieving blood pressure control and Roux-en-Y gastric bypass (RYGB) had greater effect on remission of hypertension and diabetes than laparoscopic adjustable gastric banding .
Effects of BS on pre-existing CKD and on renal function in adolescence
Although there is a relevant increase of early BS complications risk with patients with higher CKD stages when adjusted for hypertension and diabetes , the absolute incidence of complications remained <10%. Another large study found no significant increase in risk of 30-day postoperative complications after any type of BS surgery in more advanced stages of CKD .
The effect of BS in obesity-related and biopsy-proven glomerulopathy patients lies in stable creatinine clearance trend, irrespective of the presence and number of lesions at baseline, with significant reduction in hypertension and 24-hour albuminuria . Similarly, the patients with CKD stages 3 and 4 show significant post-surgery rise in eGFR, have significant rise in eGFR post-surgery, with RYGB surgery having better effects on renal function than sleeve gastrectomy . In yet another study, Japanese patients with morbid obesity and CKD stages 3 and 4 did not have significant improvement in the eGFRcys post-surgery . Even though there are possible early BS complications in terms of acute kidney injury (AKI), there are long-term BS positive effects on AKI incidence .
There is also an evident improvement in eGFR and ACR after BS surgery of obese adolescents with preoperative kidney disease , with several predictors of eGFR increase such as BMI and female sex. Importantly, renal disease should be recognised as a selection criterion for BS for severely obese adolescents, to optimize chances for reversal of severe obesity and kidney risks . Adolescent patients, as well, are more likely to have a post-surgery remission of hypertension and diabetes than adults .
Putative mechanisms behind the effects of BS on renal function
The excess of visceral fat via glomerulomegaly, hyperfiltration and glomerulosclerosis leads to obesity-mediated kidney disease, which can be ameliorated and even fully reverted at times by BS. Mechanisms such as insulin resistance, the excess of central adiposity, as well as impaired oxygen utilization contribute to hyperfiltration, which is particularly common in adolescence (Figure 1 ).