A study results showed that Roux-en-Y gastric bypass surgery increases postoperative risk for kidney stones.

Our study is not an indictment of bariatric surgery — the benefits of this surgery are well known, lead author Brian Matlaga, MD, from the Johns Hopkins University School of Medicine and James Buchanan Brady Urological Institute in Baltimore, Maryland, said in a news release. Rather, we’d like to help physicians understand that their bariatric patients could be at risk for kidney stones, a condition that could be avoidable with proper preventative care.

Previously, the occurrence of stone disease after bariatric surgery was unknown. However, mineral and electrolyte abnormalities are known to follow bariatric surgery and to increase the risk for urolithiasis. The study aimed to assess the probability of being diagnosed with or treated for an upper urinary tract stone after Roux-en-Y gastric bypass surgery.

The number of patients who underwent Roux-en-Y gastric bypass surgery was 4639 from 2002 to 2006. In addition, a control group of 4639 obese patients who did not have surgery were identified from a national private insurance claims database. All patients received 3 or more years of continuous claims data. The main endpoints of the study were diagnosis and surgical treatment of a urinary stone.

Urolithiasis was diagnosed in 7.65% (355/4639) of patients after Roux-en-Y gastric bypass surgery vs 4.63% (215/4639) of obese patients in the control group (P < .0001). Shock wave lithotripsy was more common in the Roux-en-Y group (81 [1.75%] vs 19 [0.41%]; P < .0001) as was ureteroscopy (98 [2.11%] vs 27 [0.58%]; P < .0001).

Roux-en-Y gastric bypass surgery significantly predicted being diagnosed with a urinary stone calculus (odds ratio [OR], 1.71; 95% confidence interval [CI], 1.44 – 2.04) and undergoing a surgical urinary tract procedure (OR, 3.65; 95% CI, 2.60 – 5.14).

Roux-en-Y gastric bypass surgery is associated with an increased risk of kidney stone disease and kidney stone surgery in the postoperative period, the study authors write. Clinicians should be aware of this hazard and inform patients of this potential complication. Future studies are needed to evaluate preventive measures in the high risk population.

The study limitations include those inherent to the use of an administrative claims database.

It is likely that hyperoxaluria, which has been reported to be prevalent following these surgical procedures, is one of the inciting factors in stone formation, the study authors conclude. As obesity is currently an important national health issue and bariatric surgery to treat it is increasing at a rapid rate, further studies are urgently required to better define the etiology of hyperoxaluria as well as other stone risk factors in this population.