Kidney stones are common after bariatric surgery

Abstract

Obesity, a risk factor for kidney stones and chronic kidney disease (CKD), is effectively treated with bariatric surgery. However, it is unclear whether surgery alters stone or CKD risk. To determine this we studied 762 Olmsted County, Minnesota residents who underwent bariatric surgery and matched them with equally obese control individuals who did not undergo surgery. The majority of bariatric patients underwent standard Roux-en-Y gastric bypass (RYGB; 78%), with the remainder having more malabsorptive procedures (very long limb RYGB or biliopancreatic diversion/duodenal switch; 14%) or restrictive procedures (laparoscopic banding or sleeve gastrectomy; 7%). The mean age was 45 years with 80% being female. The mean preoperative body mass index (BMI) was 46.7 kg/m(2) for both cohorts. Rates of kidney stones were similar between surgery patients and controls at baseline, but new stone formation significantly increased in surgery patients (11.0%) compared with controls (4.3%) during 6.0 years of follow-up. After malabsorptive and standard surgery, the comorbidity-adjusted hazard ratio of incident stones was significantly increased to 4.15 and 2.13, respectively, but was not significantly changed for restrictive surgery. The risk of CKD significantly increased after the malabsorptive procedures (adjusted hazard ratio of 1.96). Thus, while RYGB and malabsorptive procedures are more effective for weight loss, both are associated with increased risk of stones, while malabsorptive procedures also increase CKD risk.

Figure 1. Risk of new onset nephrolithiasis after bariatric surgery

The risk of incident stones was greater after RYGB or malabsorptive bariatric procedures, compared to matched obese controls (P<0.001 overall). Patients with restrictive procedures were not at increased risk.

Figure 2. Risk of new onset CKD after bariatric surgery

The risk of incident CKDwas greater after malabsorptive bariatric procedures compared to matched obesecontrols (P=0.004 overall). Patients were not at increased CKD risk after RYGB orrestrictive procedures.

Figure 3. Changes in urine oxalate and CaOx SS after surgery

Panel A: Urinaryoxalate increased subtly in all cases over time after bariatric surgery (◆ solid diamonds, - - - - dashed line), and more dramatically in those that developed stones (Δ open triangles, —— solid line). Mean urine oxalate was at the upper limit of the referencevalue (0.46 mmol/day) at all time points in obese controls that developed stones (○ open circles, - · - · - · - dash-dot line). Panel B: At all time points CaOx SS was highest in the post bariatric surgery patients that developed stones (Δ open diamonds, —— solid line), but still at or above the reference mean (1.77 DG) in both obese controls with stones (○ open circles, - · - · - dash-dot line) as well as post bariatric surgery patients without stones (◆ solid diamonds, - - - - dashed line).