Does Bariatric Surgery Improve Renal Function?

Abstract

Introduction:

Obesity is a health problem that is reaching epidemic proportions. The risk of developing chronic kidney disease (CKD) is higher in obese patients. Decreasing weight could translate into an improvement in renal function. In addition, renal function can be improved by the resolution of hypertension and diabetes. The main objective of this study is to analyze renal function in obese patients undergoing sleeve gastrectomy (SG).

Material and Methods:

This study is a nonrandomized, controlled retrospective review of 223 patients who underwent a minimally invasive SG at the University of Illinois Hospital and Health System between January 2008 and December 2013. In patients with CKD, renal function parameters were measured preoperatively and at 6 months postoperatively. Renal function was evaluated by GFR that was estimated using the creatinine clearance (CrCl) according to the Cockcroft–Gault (CG) equation. Statistical analysis was performed using Student's t test for continuous paired data.

Results:

The mean operative time was 84.1 min. The mean % excess weight loss (%EWL) at 6 months was 42.6%. At 6 months postoperatively, CrCl increased by 5.03 mL/min (p = 0.01) in patients with CKD. The mean serum creatinine decreased from 1.75 to 1.45 mg/dL (p = 0.01).

Conclusions:

Renal function improves 6 months after SG in patients with CKD.

Introduction

Obesity is a health problem that is increasing to epidemic proportions. More than one-third of the population in the United States is obese¹ with numbers continuing to rise.² Obesity is associated with much comorbidity, including hypertension (HTN), type 2 diabetes mellitus (T2DM), and dyslipidemia.³ It is also associated with a higher risk of developing chronic kidney disease (CKD) due to the association with renal hyperfiltration. Previous publications have demonstrated that bariatric surgery plays an important role in the management of HTN⁴ and T2DM⁵ and is more effective than lifestyle modifications and medical treatment alone.⁶

Decreased weight can lead to an improvement in renal function and an improvement in CKD. A better control of HTN and T2DM can also be achieved with weight loss.^7,8

Currently, more than 20 million Americans have CKD.⁹ Given the increasing number of obese people in the United States and around the world, the numbers of obesity-related cases of HTN, T2DM, and kidney disease are also expected to increase.⁹ The main objective of this study is to analyze the improvement in renal function in obese patients who undergo SG. In addition, the effect of SG on HTN and T2DM will also be analyzed.

Material and Methods

This study is a retrospective review of a prospectively maintained database of 223 patients who underwent a laparoscopic sleeve gastrectomy (SG) by a single laparoscopic experienced surgeon at the University of Illinois Hospital and Health Sciences System between January 2008 and December 2013. This study was conducted under institutional review board approval. All patients met the standard eligibility criteria for bariatric surgery. These patients met the National Institutes of Health guidelines for obesity with either a body mass index (BMI) greater than 35 kg/m² and weight loss recalcitrant to nonsurgical measures with two or more comorbidities or a BMI ≥40 kg/m² with no comorbidities.¹⁰ All patients were placed on a medically supervised diet and underwent formal psychological evaluation to assess their commitment and potential for adherence. Out of 223 patients, 30 were diagnosed with CKD before the surgery.

The following variables were obtained from electronic medical records from the University of Illinois Hospital and Health Sciences System: age, gender, height, weight, BMI, age at surgery, creatinine, estimated creatinine clearance (CrCl), length of surgical procedure, length of hospitalization, postoperative complications, and %excess weight loss (%EWL) at 6 months. Data were also collected on comorbidities, including HTN, T2DM, gastroesophageal reflux disease, dyslipidemia, and sleep apnea. Improvement in HTN and T2DM was noted if the patient had a decrease in daily medications at 6 months. The value of the renal function (GFR) was estimated using the CrCl according to the Cockcroft–Gault (CG) equation.¹¹

Preoperative evaluation

All patients completed a medically supervised weight loss diet for 3–6 months and received psychological evaluation. Subsequently, patients were evaluated by the bariatric surgery team to determine eligibility and potential complications.

Patients with CKD were selected to undergo a SG due to the option to be eligible for kidney transplant in the future. Among all bariatric surgeries, SG is less complex,¹² is associated with fewer complications, and is mainly a restrictive procedure, which minimizes the impact on absorption of immunosuppressive drugs.¹³

Patients were evaluated by a multidisciplinary team that comprised cardiologists, pulmonologists, and endocrinologists, if patients presented with any pertinent risk factors related to surgery.

Intraoperative and postoperative management

Standard antibiotic and antithrombotic prophylaxis was provided. Laparoscopic SGs were performed using a 36-Fr bougie and staplers with GORE SEAMGUARD^® (WL Gore & Associates).

Patients ambulated within a few hours following the procedure and started oral tolerance trial on postoperative day 1. Majority of the patients were discharged on day 2. Patients were seen in the bariatric clinic for follow-up at 6 and 12 months. A renal function test was performed at 6 months postoperatively. Clinical evaluation and adjustments to medication for HTN and T2DM were also assessed at the 6-month visit.

Statistical analyses

Data analyses were conducted using SPSS 22.0 (IBM, SPSS Statistics). Statistical analysis was performed comparing data related with renal function. In patients with CKD, renal function parameters were measured preoperatively and 6 months postoperatively. Statistical analysis was performed with Student's t test for continuous and paired data, and chi-square analysis was performed with categorical variables. Confidence intervals were set at 95%, and a two-sided p-value of <0.05 was considered statistically significant. Linear regression analysis was performed in the total sample size to adjust for age, gender, prebariatric BMI, and %EWL 6 months after surgery.

Results

Demographics and medical characteristics

The study population comprised 184 women (82.5%) and 39 men (17.5%). Patients were divided in two groups according to the renal function status. There were statistical significant differences regarding mean age with 39.9 ± 10.3 years in the normal renal function group compared with the 52.6 ± 10.9 years in the CKD group (p < 0.001). The mean BMI before SG in the normal renal function group was 51.3 ± 9.7 kg/m², showing no significant differences compared with the CKD group 51.6 ± 9.3 (p > 0.05). Out of 223 patients, 30 had CKD diagnosed at the time of the surgery. Among those 30 patients, 23 had also HTN (76.7%) and 15 had T2DM (50%), showing significant differences when comparing with the normal renal function group (p < 0.05). Patients' demographic information and comorbidities are shown in Table 1.

Table 1.

Patients' Demographic Information and Comorbidities

Variables	No CKD	CKD	p
Female	156	28	NS
Male	37	2	NS
Mean age (years)	39.9 (SD = 10.3)	52.6 (SD = 8.9)	<0.001
Mean BMI (kg/m²)	51.3 (SD = 9.7)	51.6 (SD = 9.3)	NS
Hypertension	46.2%	76.7%	<0.05
T2DM	31%	50%	<0.05
Hypercholesterolemia	26.9%	36.7%	NS
OSA	34.1%	43.3%	NS

CKD, chronic kidney disease; BMI, body mass index; NS, not significant; T2DM, type 2 diabetes mellitus; OSA, obstructive sleep apnea.

This study analyzed changes in creatinine clearance 6 months after surgery. In those patients with normal renal function before surgery, no significant differences were identified in creatinine clearance at 6 months of follow-up. However, in patients with pre-existant CKD, the creatinine clearance increased from 45.48 to 51.20 mL/min (p = 0.0031) at 6 months postoperatively, which was statistically significant. In addition, the creatinine decreased from 1.75 to 1.45 mg/dL (17.1%) at 6 months following surgery (p < 0.05). Overall, in patients with CKD, there were significant differences comparing renal function parameters before and after bariatric surgery (Table 2).

Table 2.

Mean CrCl by Different Categories and CKD Status

	CKD			Without CKD
Category	Presurgery (N = 30)	After surgery (N = 25)	p	Presurgery (N = 168)	After surgery (N = 89)	p
Overall Mean CrCl	45.48 (2.55)	51.20 (3.36)	0.0031	94.31 (1.80)	93.90 (2.52)	0.9138
HTN change
No HTN at baseline	52.46 (2.19)	63.76 (3.88)	0.0037	94.78 (2.43)	91.50 (2.96)	0.5058
HTN not decreased	43.47 (5.42)	53.81 (5.89)	0.0495	96.83 (4.50)	94.95 (5.06)	0.4080
Decreased HTN	43.26 (3.62)	44.22 (4.60)	0.4134	91.14 (3.08)	95.93 (5.29)	0.2334
T2DM change
No T2DM at baseline	49.51 (3.38)	59.76 (4.10)	0.0280	96.77 (2.29)	94.38 (3.36)	0.0966
T2DM not decreased	41.28 (5.63)	45.03 (5.83)	0.2157	90.78 (3.65)	90.55 (3.81)	0.9404
Decreased T2DM	41.54 (4.50)	45.79 (6.03)	0.1776	86.85 (4.01)	97.31 (6.60)	0.0223

The p-value is given by paired two sample t test.

CrCl, creatinine clearance; HTN, hypertension.

Analysis was also performed regarding comorbidities. While patients with associated HTN had a significant change in creatinine clearance at 6 months postoperatively, patients who did not have associated HTN also showed similar results. Regarding T2DM, results showed that creatinine clearance increased significantly in patients who did not have T2DM, while in patients with associated T2DM, the increase in creatinine clearance was not statistically significant. Furthermore, creatinine clearance improved significantly in patients whose HTN did not improve at 6 months postoperatively. Conversely, creatinine clearance did not improve significantly in patients who had a significant improvement in their HTN at 6 months postoperatively. These results indicate that improvement in comorbidities does not affect renal function in patients with CKD after SG. In patients with CKD, bariatric surgery improves renal function, regardless of improvement in comorbidities. These results are summarized in Table 2.

A regression analysis model was performed to establish a relationship between renal function and comorbidities such as HTN or T2DM. Results showed that neither of any comorbidities has any correlation with creatinine clearance in patients with CKD. These results were consistent with results from Table 2 and are summarized in Tables 3 and 4. There were no significant differences in renal function after bariatric surgery, despite comorbidities' status in patients. When adjusting comorbidities, renal function and CKD, results showed that in patients with CKD, the improvement in renal function was due to the surgery itself and it was not related to the improvement in comorbidities. These data are summarized in Table 3.

Table 3.

Association of Change of CrCl with Covariate for CKD Individuals

Outcome	Unadjusted regression coefficient	p	Adjusted ^a regression coefficient	p	Adjusted ^b regression coefficient	p
HTN category (reference group: No HTN at baseline)
HTN not decreased	−2.11	0.722	1.11	0.859	2.99	0.637
Decreased HTN	−14.54	0.035	−11.78	0.104	−9.62	0.172
T2DM category (reference group: No HTN at baseline)
T2DM not decreased	−4.61	0.395	−1.14	0.846	−3.05	0.615
Decreased T2DM	6.24	0.303	5.61	0.358	4.75	0.420

Adjusted for demographic variables, including age and gender.

Adjusted for demographic and clinical variables, prebariatric BMI and %EWL at 6 months.

%EWL, %excess weight loss.

Table 4.

Association of Change of CrCl with Covariate for Individuals without CKD

Outcome	Unadjusted regression coefficient	p	Adjusted ^a regression coefficient	p	Adjusted ^b regression coefficient	p
HTN category (reference group: No HTN at baseline)
HTN not decreased	−1.95	0.727	−3.17	0.558	−2.07	0.721
Decreased HTN	−1.79	0.789	−1.98	0.761	−2.32	0.729
T2DM category (reference group: No HTN at baseline)
T2DM not decreased	6.47	0.225	5.22	0.341	6.04	0.305
Decreased T2DM	17.49	0.017	15.68	0.029	17.82	0.021

Adjusted for demographic variables, including age and gender.

Adjusted for demographic and clinical variables, prebariatric BMI and %EWL at 6 months.

Linear regression analysis failed to demonstrate significant differences regarding perioperative and postoperative complications, operative time, and length of stay in patients with CKD.

Discussion

Obesity has been established as an independent risk factor for CKD in recent observational studies.^9,14–16 Experimental and clinical data have shown that obesity produces hyperfiltration and the glomerular hyperfiltration that can contribute to the development of CKD.¹⁷ In addition, renal damage is related with other comorbidities that can also be seen in obesity, including HTN and T2DM.

Bariatric surgery has previously been proven to be a better option for improving comorbidities⁶ as opposed to medical treatment; however, scarce literature is available regarding renal function in patients undergoing bariatric surgery. In 2009, results of a systematic review and meta-analysis showed that in patients with CKD, weight loss that was attained through nonsurgical interventions was not associated with a change in glomerular filtration.⁹ Another study showed that nonsurgical treatment with a low caloric and normoprotein diet developed a worsening of renal function and a decrease in creatinine clearance that was significant.¹⁸ However, it seems reasonable that lowering the BMI might be followed by a decrease in hyperfiltration, resulting in an improvement of renal function. Navarro-Diaz et al. have previously reported a significant improvement in renal alterations that are associated with extreme obesity (glomerular hyperfiltration, proteinuria, high albuminuria, and microhematuria) following bariatric surgery, but their study did not involve patients with CKD.¹⁷ Several studies have shown that the inflammatory and metabolic changes associated with obesity play a vital role in the development of pathological conditions of the glomeruli.^15,16 Recent studies have indicated that surgically induced weight loss is associated with a decrease in renal inflammatory markers.^19,20 The decrease in renal inflammatory markers could be one of the mechanisms contributing to the improvement in renal function after bariatric surgery.^19,20 Johnson et al. found a strong positive correlation between GFR and renal parenchymal volume (RPV).²¹ Their study also showed decreased RPV and, thus, decreased GFR in severely obese patients with hyperfiltration after undergoing weight loss therapy. RPV usually increases with increasing body size due to nephron hypertrophy to meet increased metabolic demand.²² With weight loss therapy, metabolic demands, and thus, RPV decrease in obese patients.²¹

This current study compares preoperative and postoperative creatinine clearance in patients undergoing SG who presented with CKD. Results from this study show that the creatinine clearance increases by a mean of 5.03 mL/min in patients with CKD 6 months following bariatric surgery. This result was statistically significant (p < 0.05). Overall, data showed that the improvement in renal function in those patients with CKD diagnosed was not related to the improvement of the comorbidities, but, in fact, was surgery related.

Due to the study's small sample size, retrospective approach, and nonrandomization, there is a limitation to determine the direct effect of bariatric surgery in improvement of renal function in patients with comorbid HTN and T2DM. Although all patients with comorbidities showed some degree of improvement in renal function, and both conditions also improved following bariatric surgery, further studies are needed to determine if the improvement in renal function is due exclusively to bariatric surgery (decreasing the hyperfiltration) or is due to the improvement of the associated comorbidities.

Conclusions

In our experience, bariatric surgery improves renal function (CrCl). Six months following bariatric surgery, creatinine clearance increases significantly (p < 0.05) in patients with CKD.

Footnotes

Acknowledgments

The authors thank Dr. Sergio Barroso and Jinsong Chen for their guidance, knowledge, and help.

Author Disclosure Statement

No competing financial interests exist.

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