GFR in the early postoperative period in bariatric surgery

Authors

Abstract

Aim Bariatric surgery is a treatment model for patients with a body mass index exceeding 35 kg/m² and obesity-related complications. Significant clinical benefits have been identified. Nevertheless, despite nutritional support, there is a possibility that vitamin and iron parameters may be adversely affected. We aimed to evaluate whether postoperative changes in vitamin and iron parameters affect GFR.
Materials and Methods A retrospective analysis was conducted on the renal function tests, vitamin values, and iron parameters of 145 patients who underwent bariatric surgery by sleeve gastrectomy in the preoperative, first, and third-month periods.
Results The mean age of the participants was 35.78 ± 10.14 years, with 75.2% of them being female. A statistically significant reduction in weight and BMI was observed between the preoperative and third month p<0.001. The changes in GFR, creatinine, albumin, folate, B12, ferritin, and glucose values preoperatively, at the first postoperative measurement, and the third postoperative measurement were statistically significant (p < 0.001). The age of the subjects was found to be a significant factor in the preoperative, first, and third-month GFRs in a multiple linear regression analysis (p < 0.001, 0.019, <0.001, respectively). However, the vitamin and iron parameters were not found to be effective.
Dıscussion Changes in vitamin and iron parameters had no negative effect on GFR.

Keywords

Introduction

Obesity represents a prevalent public health concern on a global scale. The term “obesity” is defined on the basis of measurements of body mass index, central obesity, and body composition. In accordance with the World Health Organisation, a body mass index of 30-34.9 kg/m² is classified as Grade I obesity, 35-39.9 kg/m² as Grade II obesity, and ≥40.0 kg/m² as Grade III obesity. It is established that a body mass index (BMI) of over 35 kg/m² is associated with an increased prevalence of comorbid conditions [1]. It has been demonstrated that there is a correlation between obesity and the development and progression of chronic kidney disease. Furthermore, obesity has been identified as a risk factor for the onset of diabetes and hypertension, exerting both direct and indirect effects on the development of these conditions [2].
The most efficacious treatment of obesity, which is a preventable risk factor that maintains long-term weight loss, is bariatric surgery [3]. The prevalence of obesity-related complications is significantly reduced following bariatric surgery. Bariatric surgery has been demonstrated to enhance renal function [4, 5]. Additionally, some studies have indicated an association between bariatric surgery and acute kidney injury and kidney stone formation [6]. The impact of bariatric surgery on the kidneys remains a topic of ongoing debate.
Nutritional deficiencies and vitamin-mineral deficiencies are known in obese patients before and after bariatric surgery [7]. Iron deficiency after bariatric surgery is especially common in menstruating women. It was also found that the risk of calcium, vitamin D, and vitamin B12 deficiency increased [8]. Vitamin D deficiency was reported to have a negative effect on renal function [9]. High blood homocysteine levels lead to decreased renal function and cardiovascular side effects. Folate and vitamin B12, which are recommended in treatment, can significantly reduce homocysteine side effects [10]. Therefore, their deficiency after bariatric surgery may adversely affect renal function. Anaemia is a risk factor for chronic kidney disease progression [11, 12].
It is anticipated that renal function will improve in conjunction with the resolution of obesity following bariatric surgery. This study was designed to investigate whether postoperative changes in vitamin and iron parameters have an impact on renal function.

Materials and Methods

The study was conducted on 145 patients who underwent sleeve gastrectomy for obesity at our hospital between 1 September 2023 and 1 May 2024. The study included patients aged between 18 and 60 years with a body mass index (BMI) over 35 kg/m² who had been approved for the operation following consultations with endocrinologists and anesthetists. The demographic data, including age and gender, and the anthropometric data, including preoperative height, weight, and BMI, along with the patient’s systolic and diastolic blood pressure, were recorded at the time of admission. The weight and BMI were also recorded in the third postoperative month. Analytical measurements, including creatinine, glomerular filtration rate (calculated with Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2021), calcium, albumin, ferritin, folate, vitamin B12, hemoglobin, transferrin saturation, and fasting glucose, were obtained from the hospital record system at the preoperative (0), first (1), and third (3) months. Following surgery, patients were provided with vitamin capsules or a liquid containing 100 mg of vitamin B1, 90 mg of vitamin C, 17 mg of iron, 16.58 mg of magnesium, 4 mg of vitamin B6, 3.4 mg vitamin B2, 600 microgram folic acid, 500 microgram vitamin B12, 400 mg biotin, and 25 microgram vitamin D, according to their preference.
Statistics
Analyses were conducted using Statistical Package for Windows 22.0 version (IBM SPSS Statistics, Armonk, NY, IBM Corp. 2013). Categorical variables were presented as frequency (n) and percentage (%). The conformity of continuous variables to normal distribution (-3,+3) was tested with Skewness and Kurtosis and expressed as arithmetic mean and standard deviation values. The quantitative data that were not normally distributed were presented as the median and interquartile range (IQR).
Normally distributed variables were evaluated using a repeated ANOVA test, while non-normally distributed variables were evaluated using a Friedman test. A Kruskal–Wallis test was conducted to assess the relationship between preoperative weight, BMI, and third-month variables. The impact of vitamin and iron parameters on GFR was assessed through multiple linear regression analysis. A p-value of less than 0.05 was considered statistically significant.
Ethical Approval
This study was approved by the Ethics Committee of Ufuk University Non-Interventional Clinical Research Evaluation (Date: 2024-06-11, No: 24.06.02.03).
In the retrospective study, consent was obtained from the patients who could be reached. This was made in accordance with the Helsinki principles.

Results

The mean age of the participants was 35.78 ± 10.14 years, with 75.2% of them being female. A statistically significant reduction in weight and BMI was observed between the preoperative and third month (p < 0.001). The demographic and anthropometric data of the study group are presented in Table 1.
The observed decline in GFR during the first month and subsequent increase during the third month were found to be statistically significant (p < 0.001). The decline in creatinine levels observed in the third month following the initial increase in the first month was statistically significant (p < 0.001). The decline in albumin levels observed in the first and third months was statistically significant (p < 0.0001). The decline in hemoglobin levels observed in the initial and subsequent months was not statistically significant (p = 0.24). The observed increase in vitamin D values during the first and third months did not reach statistical significance (p = 0.42). The observed increase in calcium levels during the first month and the subsequent stability during the third month were found to be statistically significant (p < 0.001). The transferrin saturation levels demonstrated a decrease in the initial month and an increase in the subsequent month. However, this change was not statistically significant (Table 2, Figure 1). The increase in folate, ferritin, and B12 variables in the first month and the decrease in the third month were statistically significant (p < 0.001). The decrease observed in the glucose variable in the first month continued with a partial increase in the third month, which was statistically significant (p < 0.001) (Table 2, Figure 1).
In the multiple linear regression analysis of vitamin and iron parameters, which examined the effects on GFR after bariatric surgery, age was identified as an effective independent variable on GFR in the preoperative, first, and third months. The results demonstrated that the increase in the value of vitamin B12 in the first month had minimal effect on GFR (β: 0.387, 95% Alb1 145 CI 0.007-0.047, p = 0.009). Furthermore, the 95% confidence intervals for the beta coefficients indicated that the effects of age on GFR were statistically significant in the preoperative, first and third months (β: -0.758, 95% CI -1.117 -0.794, p<.001; β: -0.394, 95% CI -0.972-0.092, p = 0.019; β: -0.554, 95% CI-1.212-0.405, p < 0.001). No statistically significant effect was observed for the other parameters (Table 3).

Discussion

The objective of this study was to investigate the immediate effects of changes in vitamin and iron parameters on glomerular filtration rate in patients undergoing sleeve gastrectomy for obesity. The study was conducted over three months, with assessments made at the preoperative stage, at one month post-surgery, and at three months post-surgery. The findings indicated that changes in vitamin and iron parameters did not result in any negative effects on renal function within the short- term period.
It is established that obesity, which is recognized as a risk factor in the development and progression of chronic kidney disease, hurts renal function when present alongside other conditions such as hyperfiltration, inflammation, diabetes, and hypertension. In a two-year follow-up study, Magalhaes et al. [13] observed an increase in GFR levels and a decrease in microalbuminuria levels in bariatric surgery patients with a GFR above 30ml/min/1.73m². In the present study, the slight decrease in GFR observed in the first month may be attributed to acute metabolic changes occurring in the postoperative period, as well as the transient impact of rapid weight loss and the loss of muscle and adipose tissue on the glomerular filtration rate. It is established that hyperfiltration tends to improve with weight loss. The observation that the glomerular filtration rate approached the baseline level in the third month indicates that metabolic balance was restored, and the renal burden was relieved with weight loss. The analysis of GFR distribution ratios indicated a more homogeneous distribution in the third month, which suggests that metabolic balance was regulated. The results of our short-term study were found to be consistent with those of the two-year follow-up study.
Nutritional deficiencies and vitamin-mineral deficiencies are known in obese patients before and after bariatric surgery [7]. The glomerular filtration rate, which is expected to be affected by postoperative metabolic and hemodynamic changes in patients undergoing bariatric surgery, is also expected to be affected by changes in micronutrient levels, including vitamin and iron parameters. Postoperative nutrient deficiency may affect GFR [10], who reported that high homocysteine levels decreased GFR, investigated the effects of homocysteine, folate, and cobalamin on renal function. They reported that treatment to decrease homocysteine levels would be beneficial in the preservation of renal function. Folate deficiency may lead to an increase in homocysteine and increase the risk of endothelial dysfunction and vascular damage. The present study did not reveal any reduction in folate levels among participants who were administered a polyvitamin supplement to prevent folate deficiency. No discernible impact of folate levels on the enhancement of GFR was observed at the end of the third month. In the multiple regression analysis, in which the increase in vitamin B12 in the first month and its partial decrease in the third month were evaluated, it was found that this had a minimal effect on renal function. The Mendelian randomization study by Park et al. [10] reported that vitamin B12 was not effective. Our study data may not have shown a relationship due to an insufficient number of subjects and a short follow-up period.
A deficiency of vitamin D may be a common occurrence following bariatric surgery. In this case, changes in calcium and parathormone levels may occur, which could indirectly affect GFR. Furthermore, deterioration of renal function may occur in conjunction with nephrocalcinosis. A study conducted to understand the physiology of deficiency in the absorption of vitamins, minerals, and drugs in different surgical applications following bariatric surgery reported that vitamin D and calcium deficiency were frequently observed [14]. They reported that preoperative vitamin D deficiency was observed in 60% of patients and was secondary to 25-hydroxyvitamin D absorption and clearance by adipose tissue. Consequently, they observed an acute and transient increase in systemic concentrations of vitamin D during the initial postoperative month. The observed increase in vitamin D levels during the first month and the subsequent stability observed during the third month did not reach statistical significance. In the case of calcium, the increase observed in the first month and the subsequent stability in the third month were both statistically significant. The data obtained in our study were consistent with those reported for the first month of the study mentioned above. The impact of vitamin D on GFR was not statistically significant.
Ferritin is an important indicator of iron metabolism and is expressed as a measure of iron stores. Iron deficiency anemia is a common consequence of sleeve gastrectomy, resulting from a reduction in food intake and malabsorption. In the present study, the abrupt elevation in ferritin levels during the initial month was regarded as an acute phase reaction. It is recommended that ferritin be evaluated in conjunction with transferrin saturation. Anemia may result in a reduction in GFR due to hypoxia and oxidative stress. This study did not observe any short-term effect on GFR despite significant fluctuations in ferritin levels. In the study conducted by Saundhu et al. [15], no change was observed in any vitamin or iron parameters, with the exception of a 20% postoperative increase in vitamin B12 in bariatric surgery patients who were compliant with nutritional support. These findings are consistent with those of our study.

Limitations

The results of this study demonstrate the effects of sleeve gastrectomy on renal function in the short term. It is important to consider the limitations of the study. The limited sample size, the fact that the data results cover the short term, and the fact that long-term results were not evaluated prevent the generalizability of these results. Further investigation is required to determine whether the observed changes in vitamin and iron parameters have an impact on renal function in the short term. It would be beneficial to evaluate this in a larger patient group.

Conclusion

It is possible that deficiencies of vitamins, particularly folate and vitamin D, may exert indirect effects on renal function following sleeve gastrectomy. Iron deficiency anemia has been demonstrated to have a deleterious impact on renal function. In this study, the glomerular filtration rate, which exhibited a decline in the first month, demonstrated a tendency towards improvement in the third month. This suggests that fluctuations in vitamin and iron parameters did not exert a significant influence on renal function within the short term. Nevertheless, the long-term failure to correct vitamin and iron deficiencies may have an adverse impact on renal function. Therefore, it can be concluded that close monitoring of micronutrient levels in sleeve gastrectomy patients and supplementation when necessary may be an important factor in the protection of renal function.

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