Journal Club; For educational purpose only.

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.