Does bariatric surgery improves kidney function? A cohort study

Weight loss of This cohort It was randomly 35 who underwent bariatric (12 and with of at The ranged from and Those with and with renal with microalbuminuria ≥ 30mg/dL, were excluded. Serum levels of creatinine and cystatin C were measured, and the glomerular ltration rate (GFR) was estimated using the CKD Epi (chronic kidney disease epidemiology collaboration) cystatin-creatinine equation. The investigation Committee.


Conclusion
It was observed improvement of the majority of morbidities after bariatric surgery, as well as renal function, in obese individuals. Despite these results, larger and longer term outcome cohorts are required for better answer of the main purpose of this health issue.

Background
Obesity is an abnormal or excessive fat accumulation that may impair health. It is most commonly assessed using body mass index (BMI), a simple and quick anthropometric tool that has a low cost. BMI ≥30 kg/m 2 is considered obesity [1].
Obesity is a global epidemic, affecting all age, race and ethnic groups. Nowadays, overweight and obesity represent over one third of the planet population. It increases the risk for many chronic diseases, such as diabetes mellitus, cardiovascular diseases, cancers and chronic kidney disease (CKD), which may impair renal function [2][3][4][5][6][7][8][9].
In ammations, oxidative stress and hyper activation of renin/angiotensin/aldosterone system, besides leptin and adipocin may play an important role in the physiopathology of renal dysfunction in obese patients. One can observe increase renal sodium reabsorption, besides the recruitment of functional reserve with glomerular hyper ltration. Obesity can also promote hypo ltration, increasing the risk for CKD [10][11][12][13][14][15][16][17].
Aiming to reduce the risk of obesity and its morbidities, as well as improving life quality of these individuals several clinical and surgical approach have been used including change in life style, drugs and surgical interventions. Bariatric surgery has become the main operative way of controlling the associated morbidities, and an effective method for achieving sustained weight loss, improves blood pressure, reducing hyperglycemia, and even inducing diabetes remission [18][19][20][21][22].
The effect of bariatric surgery regarding the renal function is a subject of intensive research. In some papers one can observe, after this operative procedure, improvement of glomerular ltration rate (GFR), reduction of hyper ltration and decrease in the micro albuminuria, preventing the onset of CKD and its progression. But in others, the improvement of kidney function is not well clear [23][24][25][26].
The purpose of this study was to evaluate the impact of bariatric surgery on renal function of the patients using a more sensitive biological marker.

Methods
An observational, longitudinal and analytical study (cohort) was performed. The patients who participated in the study signed an informed consent form, after study approval by the Ethics Committee of the Faculty of Medical Sciences -UNIFACISA -Campina Grande-Paraíba, Brazil.
The criteria for performing bariatric surgery followed the recommendation of the National Consensus of Health Institutes with body mass index (BMI) ≥ 40kg/m2 without comorbidities or ≥ 35kg/m2 associated with comorbidities. BMI was obtained by weight, in kilograms, divided by height, by meter squared, and classi ed according to the values established by the World Health Organization (WHO).
It was randomly enrolled 35 patients who underwent bariatric surgery (12 bypass and 23 sleeve) with follow-up of at least one year, with ages from 24 to 57 years of age. Those with thyroid disease and renal disease with microalbuminuria ≥ 30mg/dl were excluded.
The weight was measured using Tanita BC533® portable scale (Brazil), with the patient standing and barefoot, in light clothes and without props. Height was measured by Altur-aexata® (Brazil), with the subject standing, barefoot, with heels together, back straight and arms extended at the side of the body.
Blood samples were collected in the morning after a fasting period of at least 12 hours.
The creatinine dosage was performed by the Jaffé reaction, with a result expressed in mg/dl, from the isotope dilution mass spectrometry (IDMS) methodology, according with organizations involved with laboratory quality management programs, for monitoring of total analytical error linked to the method.
The cystatin C was measured by nephelometry and later calibrated to recent cystatin C standardization, with a result expressed in mg/l.
The estimated glomerular ltration rate (GFR) was calculated using Nefrocalc 2.0 through the CKD-EPi equation cystatin-creatinine. After the calculation of the GFR, a correction was made for the corresponding body surface [27]. It was de ned normal GFR between 90 and 120 mL/min/1.73 m2, hypo ltration was de ned by GFR<90 mL/min/1.73 m2 and hyper ltration was de ned by GFR The samples were gathered at random from the obesity outpatient department when they were coming for the preoperative period and at least one year post-operative follow-up.
Quantitative variables were expressed by their means and standard deviation and qualitative variables were expressed by their absolute and relative frequencies. These parameters were fed into excel spreadsheets, and then analyzed using GraphPad InStat3 software. The paired "t" test was used for assessing difference between means. Fisher exact test was used to evaluate possible differences between frequencies. P ≤ 0.05 was established for rejection of the null hypothesis.

Discussion
Obesity, as human being earth problem, has been continually increasing its prevalence, as well as its associated comorbidities and health care costs. Effective management of obesity and early intervention measures are necessary to overcome this global issue. The responsibility for preventing and managing this global epidemic does not lie solely on an individual, but also on the entire society and the health care systems [3,4].
Multidisciplinary approaches for obesity management and the collaboration among clinical physicians, endocrinologists, nutritional professionals, physiotherapists, psychiatrists, surgeons and nurses need to be improved across the whole globe to tackle this huge health issue, which great affect the life quality [1].
Bariatric surgery remains the best strategy for the management of obesity regarding to effective and sustained weight loss. One can observe in this study, a signi cant weight lost after at least one year follow-up of these patients, as indicated in several studies [18][19][20][21][22]29].
As regard to comorbidities (blood hypertension and diabetes) one can observe signi cantly decrease of the prevalence of these diseases after bariatric surgery, similar to most studies [18][19][20][21][22]30]. Similarly, there was improvement of sexual dysfunction, especially among those who could control anxiety and depression [31].
Cystatin C has been used as biological marker for renal function due to its high sensitivity and speci city and it is not in uenced by weight loss [28, [32][33][34], reasoning because it was used for assessing renal function after bariatric surgery in obese patients in the present study.
Studies have pointed the improvement of renal function after bariatric surgery, either with increased glomerular ltration rate in patients with chronic kidney disease, or reduction of hyper ltration in patients with no evidence of kidney disease. In this regard, the present results give support to this evidence, which can summarized in improvement of renal function after bariatric surgery [23][24][25][26][27]35].
Renal function improvement was more evident among the patients who underwent sleeve technique. However, whether any kind of bariatric surgery delays the deterioration progression of this crucial biological function is still in question, large randomized prospective studies with a longer follow-up are needed [36].
Recent data, in obese adolescents, indicate that patients who require bariatric surgery may need a more personal technique as part of medicine precision for protecting kidney function, especially when long term outcome is anticipated. Furthermore, future non-surgical interventions therapies may mitigate the morbidities associated with obesity [37].

Limitations
First, the sample size is too small for de nitive evidence on this important question. Second, the follow-up time could not be su cient for assessing renal function after bariatric surgery in obese patients. Even though, the study has made a contribution for this challenging and unsolved question -Does bariatric surgery improve kidney function? Availability of data and materials

Conclusion
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Figure 1
Modi cations in GRF after bariatric surgery. The majority of patients improved their glomerular ltration rate.