Bariatric surgery, especially malabsorptive procedures like Roux-en-Y gastric bypass, significantly increases the risk of kidney stones compared to obese controls. The risk is highest with malabsorptive procedures and correlates with the degree of fat malabsorption and enteric hyperoxaluria. However, bariatric surgery does not appear to increase the risk of chronic kidney disease. Further research is still needed to fully understand the mechanisms by which bariatric surgery leads to hyperoxaluria and kidney stone formation.

1. Bariatric Surgery and Kidney Stones
Wisit Cheungpasitporn
August 21, 2015

2. Disclosure
• None

3. Increasing proportion of adults with obesity,
United States, 1990 to 2010
*obesity was defined as a BMI ≥ 30 kg/m2
In 2012, more than one-
third (34.9% or 78.6
million) of U.S. adults
are obese.

4. Indications for Bariatric Surgery
• Bariatric surgery is a treatment option for people with obesity if all
of the following criteria are fulfilled:
• BMI ≥40 kg/m2
, or
• BMI 35 - 40 kg/m2
and other significant diseases (for example,
such as type 2 DM, HTN or OSA) that could be improved if
they lost weight.
• All appropriate non-surgical measures have been tried but the
person has not achieved or maintained adequate, clinically
beneficial weight loss.
• The person is generally fit for anesthesia and surgery.
• The person commits to the need for long-term follow-up.
NICE clinical guideline. Issued: November 2014
Fried, M. et al. Obes. Surg. 24, 42–55 (2014).

5. Classification of Bariatric Surgery
• Purely Restrictive
• Adjustable gastric banding [AGB]
• Vertical banded gastroplasty [VBG]
• Sleeve gastrectomy
• Purely Malabsorptive
• jejuno–ileal bypass
Frühbeck G. Nat Rev Endocrinol. 2015;11(8):465-77

6. Classification of Bariatric Surgery
• Mixed restrictive and malabsorptive
• Restrictive > Malabsorptive
• Roux-en-Y gastric bypass [RYGB]
• Malabsorptive > Restrictive
• Biliopancreatic diversion with or without
duodenal switch
• Very, very long limb RYGB
Frühbeck G. Nat Rev Endocrinol. 2015;11(8):465-77

7. Mechanick JI et al. Obesity. 2013;21 Suppl 1:S1-27.
Laparoscopic adjustable gastric banding

8. Sleeve gastrectomy
Tarplin S et al. Nat Rev Urol. 2015;12(5):263-270

9. Roux-en Y gastric bypass‑
Tarplin S et al. Nat Rev Urol. 2015;12(5):263-270

10. Lieske JC et al. Semin Nephrol. 2008;28(2):163-73.
Roux-en Y gastric bypass‑

11. Biliopancreatic diversion with duodenal
switch
Lieske JC et al. Semin Nephrol. 2008;28(2):163-73.

12. Association Between Bariatric Surgery
and Long-term Survival
Arterburn DE et al. JAMA . 2015;313(1):62-70.
2.4%
6.4%
1.7%
10.4%
23.9%
13.8%
Matched control
Surgical patients
Bariatric procedures: 74% gastric bypass, 15% sleeve gastrectomy, 10%
adjustable gastric banding, and 1% other.
Matched age, sex, geographic region, BMI, diabetes,
and Diagnostic Cost Group

13. Frühbeck G. Nat Rev Endocrinol. 2015;11(8):465-77

14. Chang SH et al. JAMA Surg. 2014;149(3):275-87
BMI loss within 5 years after surgery

15. Number of bariatric surgeries performed in the U.S.
Gonzalez RD et al. Curr Urol Rep;2014:15:401

16. Trends in number of procedures worldwide:
from 2003 to 2008 to 2011 to 2013
Angrisani L. et al. Obesity surgery (2015): 1-11.

17. Trends in percentage of procedures worldwide:
from 2003 to 2008 to 2011 to 2013
Angrisani L. et al. Obesity surgery (2015): 1-11.

18. Countries where >10,000 procedures were
performed in 2013 include
• United States and Canada (n = 154,276)
• Brazil (n = 86,840)
• France (n = 37,300)
• Argentina (n =30,378)
• Saudi Arabia(n =13,194)
• Belgium(n = 12,000)
• Israel (n =11,452)
• Australia/New Zealand (n =10,467)
• India (n =10,002)
Angrisani L. et al. Obesity surgery (2015): 1-11.

19. Powell CR et al. Urology. 2000;55(6):825-30.

20. Currie A et al. Obes Surg. 2011;21(4):528-39.

21. Asplin JR. Adv Chronic Kidney Dis. 2009;16(1):11-20

22. Currie A et al. Obes Surg. 2011;21(4):528-39.

23. Currie A et al. Obes Surg. 2011;21(4):528-39.

24. Obesity
CKD
Kidney Stones
Bariatric Surgery
?
?
↑
↑

25. Nazzal L, Puri S, Goldfarb DS. Nephrol Dial Transplant. 2015 [Epub ahead of print]

27. Sinha MK et al. Kidney Int. 2007;72(1):100-7.

28. Semins MJ et al. Urology. 2010;76(4):826-9.
54 subjects after RYGB; 18 patients after restrictive bariatric; 14 gastric banding and 4 sleeve gastrectomy
The mean time from restrictive surgical procedure to urine collection was 12.4 months (range: 7-30)

29. Semins MJ et al. Urology. 2010;76(4):826-9.
35.4
60.7
32.9
37.2

30. Gonzalez RD et al. Curr Urol Rep (2014) 15:401
Kidney Stone incidence following Bariatric Surgery

31. Obesity
CKD
Kidney Stones
Bariatric Surgery
↑↑↑
?
↑
↑

32. Ahmed MH et al. Nephrol Dial Transplant. 2010;25(10):3142-7.

34. Ahmed MH et al. Nephrol Dial Transplant. 2010;25(10):3142-7.

35. Neff KJ et al. Nephrol Dial Transplant. 2013;28 Suppl 4:iv73-82.

36. Obesity
CKD
Kidney Stones
Bariatric Surgery
↑↑↑
?
↑
↑

37. Lieske JC et al. Kidney Int. 2015 Apr;87(4):839-45.

38. Objective
• To compare the incidence of stones in patients
after bariatric surgery with that in comorbidity-
matched obese controls in a population based
study

39. Methods – Study population
• Bariatric surgery group
• Olmsted County residents with BMI > 35 kg/m2
, who
underwent bariatric surgery at Mayo Clinic between the
year 2000 and 2011
• Control group
• Sampled from among all Olmsted County residents with
BMI > 35 kg/m2
who were seen at Mayo Clinic during
study period
• Matched for sex, index year* and BMI with ± 3.
• 759 of 762 surgery cases were matched, with 95%
having an age within 5 years
*index year (BMI date in controls closest to preoperative BMI in surgery patients)

40. Methods - Outcomes
• Using REP* data to capture kidney stone and CKD events
for both surgery and control groups
• EMR for 24-hr urine studies
• Bariatric surgery group: as part of routine follow-up visits
beginning 6 months post surgery or at the time of a
nephrology stone clinic visit if they developed stones
• Control group: available only at the time of a nephrology
stone clinic visit
Outcome ICD-9
Kidney/bladder
stone
592, 594, 274.11
CKD 250.4, 274.10, 274.19, 403, 404,
446.21, 453.3, 572.4, 581, 582, 583,
585, 586, 587, 593.89, 593.9, 753.1,
753.0, 753.3, 791.0
*REP= Rochester Epidemiology Project

41. Methods – Statistical Analysis
• Association between bariatric surgery with a
subsequent kidney stone event and CKD
• Kaplan-Meier plots
• Cox proportional hazard models with adjustment for
age, sex, and other baseline comorbidities
• Subjects with prevalent kidney stones were excluded
from analysis of incident stones

42. Results
2683 bariatric surgery
-63 no research
authorization
-1832 non-OC
residents
-26 BMI < 35
762 bariatric surgery studied
13256 OC residents with BMI > 35
-699 bariatric
surgery
-63 no research
authorization
12494 potential control
759 matched bariatric
surgery patients
759 matched control
*OC = Olmsted County

43. Type of bariatric surgery 2000-2011
• Standard RYGB (n=591): most common (78%)
• Majority: open surgery before 2007, laparoscopic after 2004
• Malabsorptive procedure (n=105)
• Very, very long limb RYGB (n=55)
• Biliopancreatic diversion/switch (n=50)
• Restrictive procedure (n=56)
• Laparoscopic banding (n=43)
• Laparoscopic sleeve gastrectomy (n=13)

46. P=0.02 for comparison between post-bariatric group and obese stone former

48. Univariate and multivariate models of hazard ratios for kidney stones
Risk Factor HR 95% CI P
Univariate
Age at time of surgery 1.003 0.986-1.020 0.72
Sex 1.243 0.791-1.951 0.34
Hypertension 1.092 0.756-1.577 0.64
Diabetes 1.797 1.226-2.635 0.003
Arthritis 2.227 1.538-3.223 <0.001
Sleep apnea 1.617 1.118-2.341 <0.001
RYGB 2.554 1.655-3.940 <0.001
Malabsorptive 5.292 3.038-9.221 <0.001
Restrictive 0.588 0.080-4.317 0.60
Multivariate
Age 0.999 0.980-10.18 0.94
Sex 1.085 0.674-1.748 0.74
Hypertension 0.852 0.562-1.291 0.45
Diabetes 1.656 1.096-2.502 0.02
Arthritis 1.312 0.844-2.040 0.23
Sleep apnea 1.084 0.716-1.642 0.70
RYGB 2.140 1.291-3.547 0.003
Malabsorptive 4.036 2.073-7.860 <0.001
Restrictive 0.521 0.070-3.875 0.52

49. Risk of recurrent stone
• Patients with history of a prior stone at the time of
bariatric surgery were more likely to develop a
stone after surgery than non-prevalent cases (42%
vs. 14% at 10 years; HR 4.1, P<0.001)
• The risk of prevalent obese patients forming a
second stone was slightly higher (52% at 10 year)
• This reflect stone event risk to increase as the
number of prior event increases
• This does not suggest that bariatric surgery
disproportionately augments stone risk among
those with past stone events

50. Bariatric surgery was not a risk factor for developing CKD (HR 0.95; 95% CI
0.67-1.35)

52. Univariate and multivariate models of hazard ratios for CKD
Risk Factor HR 95% CI P
Univariate
Age at time of surgery 1.040 1.023-1.058 <0.001
Sex 1.716 1.716-1.143 0.009
Hypertension 2.058 1.437-2.947 <0.001
Diabetes 3.609 2.541-5.125 <0.001
Arthritis 1.075 0.747-1.547 0.70
Sleep apnea 1.470 1.036-2.085 0.03
RYGB 0.775 0.523-1.149 0.20
Malabsorptive 2.018 1.197-3.402 0.009
Restrictive 0.793 0.193-3.263 0.75
Multivariate
Age 1.026 1.006-1.045 0.01
Sex 1.219 0.788-1.886 0.37
Hypertension 1.335 0.899-1.985 0.15
Diabetes 2.903 2.003-4.207 <0.001
Arthritis 0.931 0.587-1.477 0.76
Sleep apnea 0.975 0.658-1.446 0.90
RYGB 0.750 0.469-1.201 0.23
Malabsorptive 2.044 1.087-3.843 0.03
Restrictive 0.918 0.219-3.845 0.91

54. Changes in urine oxalate and CaOx SS after surgery

55. Discussion
• The risk for kidney stones is approximately doubled in
patients after RYGB compared with matched, non-
operated, obese controls.
• The risk for kidney stones
• Malabsorptive > Standard RYGB> Restrictive

56. Discussion
• The mechanism(s) by which RYGB patients
develop hyperoxaluria is yet to be fully
explained.
• The distal malabsorptive so-called very, very
long limb RYGB or the biliopancreatic
diversion/duodenal switch, may predispose to
clinically important fat malabsorption, leading to
enteric hyperoxaluria.

57. Discussion
• The extent of hyperoxaluria corresponds to the
degree of steatorrhea.
• In the one stone clinic patient in whom fat
malabsorption was assessed, 72-h fecal fat
excretion was increased (57 g; normal <7 g),
despite the absence of diarrhea.
McLeod RS, Churchill DN. J Urol 1992; 148: 974–978
Sinha MK et al. Kidney Int 2007; 72: 100–107.

58. Discussion
• The prevalence and risk factors for oxalate
nephropathy after RYGB are less certain.
• The presence of CKD before RYGB may be an
important predisposing factor.
Nasr SH et al. Clin J Am Soc Nephrol. 2008;3(6):1676-83.

59. Limitations
• Kidney stones, CKD, and comorbidities were
determined by diagnosis codes, and laboratory
data were available for only a subset of all
patients with or without kidney stones.
• The incidence and prevalence of CKD post-
bariatric surgery might also have been
underestimated because of the effects of weight
loss on creatinine generation and serum
creatinine levels.

60. Conclusion
• Obese patients who undergo RYGB have an
increased risk for kidney stones that is
approximately double that of obese,
nonoperated controls.
• Patients with malabsorptive bariatric procedures
appear at greatest risk for stones but are also at
increased risk for new-onset CKD.

61. Questions & Discussion

62. Tarplin S et al. Nat Rev Urol. 2015;12(5):263-270

63. Cossey LN et al. Am J Kidney Dis 2013; 61: 1032–1035

64. Canales BK et al. Surg Obes Relat Dis. 2014;10(4):734-42.