Predicting the Glomerular Filtration Rate in Bariatric Surgery Patients

Abstract

Background/Aims: Identifying the best method to estimate the glomerular filtration rate (GFR) in bariatric surgery patients has important implications for the clinical care of obese patients and research into the impact of obesity and weight reduction on kidney health. We therefore performed such an analysis in patients before and after surgical weight loss. Methods: Fasting measured GFR (mGFR) by plasma iohexol clearance before and after bariatric surgery was obtained in 36 severely obese individuals. Estimated GFR was calculated using the Modification of Diet in Renal Disease equation, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation using serum creatinine only, the CKD-EPI equation using serum cystatin C only and a recently derived equation that uses both serum creatinine and cystatin C (CKD-EPI_creat-cystC) and then compared to mGFR. Results: Participants were primarily middle-aged white females with a mean baseline body mass index of 46 ± 9, serum creatinine of 0.81 ± 0.24 mg/dl and mGFR of 117 ± 40 ml/min. mGFR had a stronger linear relationship with inverse cystatin C before (r = 0.28, p = 0.09) and after (r = 0.38, p = 0.02) surgery compared to the inverse of creatinine (before: r = 0.26, p = 0.13; after: r = 0.11, p = 0.51). mGFR fell by 17 ± 35 ml/min (p = 0.007) following surgery. The CKD-EPI_creat-cystC was unquestionably the best overall performing estimating equation before and after surgery, revealing very little bias and a capacity to estimate mGFR within 30% of its true value over 80% of the time. This was true whether or not mGFR was indexed for body surface area. Conclusions: In severely obese bariatric surgery patients with normal kidney function, cystatin C is more strongly associated with mGFR than is serum creatinine. The CKD-EPI_creat-cystC equation best predicted mGFR both before and after surgery.

Change in Multiple Filtration Markers and Subsequent Risk of Cardiovascular Disease and Mortality

“…Al-though not yet widely used in clinical practice, cystatin C and b 2 -microglobulin are low molecular weight proteins considered to be filtration markers that are strongly associated with clinical outcomes (11)(12)(13). Use of these alternative filtration markers instead of or in addition to creatinine could improve estimation of GFR and prognosis in CKD (14)(15)(16)(17)(18). The use of multiple filtration markers may ameliorate bias introduced by non-GFR determinants and reduce imprecision caused by measurement error.…”

Can Bariatric Surgery Be a Surgical Treatment to Prevent the Progression of Chronic Kidney Disease?

“…Glomerular filtration rate was calculated based on both serum creatinine and serum cystatin C. However only glomerular filtration rate based on cystatin C was associated with decreased glomerular filtration rate in hypertensive women with CKD [35]. Regarding the value of cystatin C as a marker for predicting GFR in obese patients, the study by Friedman et al [36] suggested that the Chronic Kidney Disease Epidemiology Collaboration equation using both serum creatinine and cystatin C (CKD-EPIcreat-cystC) equation best predicted mGFR both before and after bariatric surgery in obese patients with kidney function for which cystatin C is more significantly associated with mGFR than is serum creatinine. Therefore, Cystatin C can be an alternative method to evaluate the changes in the eGFR in obese population since it is independent from the lean body mass or weight loss [37].…”

Is Bariatric Surgery an Effective Treatment for Type II Diabetic Kidney Disease?

“…First and foremost, postsurgical regression of diabetes is expected to retard or possibly even reverse the still incompletely understood mechanisms through which chronic dysglycemia damages the kidney. In addition, putative risk factors for kidney disease, like hypertension, hyperinsulinemia and insulin resistance, dyslipidemia, and glomerular hyperfiltration, are also improved after surgery (20,(24)(25)(26)(27). However, the literature in this area is presently too handicapped by limitations-small sample sizes, relatively short-term followup periods, lack of control groups, and inclusion of patients identified as having DKD solely on the basis of elevations in albuminuria or proteinuria-to tease out how, if at all, bariatric surgery improves DKD.…”

“…Although these findings seem to be salutary on the surface, their implications are uncertain, because they may simply be reflecting changes in renal physiology unrelated to the pathophysiology of DKD. For example, the reduction in proteinuria and albuminuria could be caused by lower glomerular filtration that is commonly seen after bariatric surgery (26). Whether this represents a protective effect against DKD is not known (28).…”

“…Whether this represents a protective effect against DKD is not known (28). Similarly, the observed improvement (i.e., drop) in serum creatinine is most likely caused by loss of lean body mass (and subsequent reduced generation of creatinine) that coincides with large weight loss rather than a clear effect on glomerular filtration (26).…”