SAN DIEGO – Patients taking calcium supplementation after gastric bypass surgery had higher rates of kidney stone growth, compared with those who received no calcium supplementation, results from a single-center retrospective study showed.
In addition, the majority of stones in patients taking calcium supplementation were comprised of calcium oxalate monohydrate, which is less amenable to extracorporeal shockwave therapy. “You need more invasive procedures to break up these kinds of stones,” lead author Christopher Loftus said in an interview at the meeting of the Endocrine Society, where the study was presented during a late-breaking abstract session.
Though it has been demonstrated that bariatric surgery is associated with an increased risk of kidney stone formation (Kidney Int. 2014 [doi:10.1038/ki.2014.352]), Mr. Loftus, a fourth-year medical student at Cleveland Clinic Lerner College of Medicine, and his associates set out to determine whether calcium supplementation increases the risk of nephrolithiasis in 60 stone-forming patients after gastric bypass surgery performed at the Cleveland Clinic. For each patient, two unenhanced CT scans at least 1 month apart and less than 2 years apart were selected at the start of the supplementation date and after the gastric bypass surgery date. The researchers calculated the rate of stone growth by the change in consecutive stone burden (the sum of maximum diameters of stones) divided by the elapsed time between scans.
Of the 60 patients, 31 received postoperative calcium supplementation (an average of 500 mg/day) and 29 did not. Compared with patients who did not take calcium supplementation, those who did were younger (a mean of 53 years vs. 58 years, respectively), more likely to be female (81% vs. 69%), and had a higher body mass index (34.5 kg/m2 vs. 32.7 kg/m2). In addition, a greater proportion of patients taking calcium supplements underwent Roux-en-Y bypass (83% vs. 64%; P = .19), had stones comprised of calcium oxalate (81% vs. 67%; P = .56), and a higher rate of stone growth (more than 10 mm/year vs. less than 5 mm/year; P = .0004). “We weren’t expecting such a pronounced effect,” Mr. Loftus said.
In their abstract, the researchers said that further studies are required to elucidate the exact role of calcium supplementation on stone disease in this patient population.
The study was funded in part by a grant from the American Society of Nephrology. Mr. Loftus reported having no relevant financial conflicts.
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