Changes in renal function following Roux-en-Y gastric bypass: a prospective study.

Background: Studies of the impact of Roux-en-Y gastric bypass (RYGB) on renal function have shown mixed results. We constructed this prospective repeated-measures controlled study to characterize this response and identify the best method of gauging renal function in this setting.

Methods: Clinical data, serum creatinine (SC), and 24-h urine were collected 1 week before and 6 months following RYGB. Glomerular filtration rate (GFR) was calculated utilizing the Modification of Diet in Renal Disease formula. Creatinine clearance (CCL) was measured as a 24-h collection (24 CCL) and calculated by the Cockcroft-Gault (CG) formula.

Results: The study population of 37 patients (81% women) had a mean age of 47 ± 11 years, had mean BMI of 47.6 ± 6.3 kg/m(2), and achieved a mean % excess weight loss (EWL) of 60.9 ± 17.1%. SC decreased from 0.83 ± 0.21 mg/dl to 0.72 ± 0.16 mg/dl (p < 0.001) and mean GFR improved from 91.6 ± 29.7 ml/min/1.73 m(2) to 104.9 ± 23.5 ml/min/1.73 m(2) (p < 0.01). Preoperatively, CG significantly overestimated CCL when compared with 24 CCL (197.1 ± 88.2 ml/min vs. 136.5 ± 53.0 ml/min, p < 0.001). In all patients, improvement in 24 CCL correlated with EWL (r = 0.32) and %EWL (r = 0.16), and significantly correlated with decrease in BMI (r = 0.51, p < 0.005). In hypertensive patients, improvement in 24 CCL significantly correlated with EWL (r = 0.43, p < 0.05), %EWL (r = 0.40, p < 0.05), and decrease in BMI (r = 0.60, p < 0.001) and was negatively correlated with age (r = -0.45, p < 0.05).

Conclusions: This study demonstrates that renal function improves following RYGB and is best identified by change in GFR. Improvement in 24 CCL is correlated with the EWL success of the patient, especially hypertensive patients.