Table 1

Baseline data for CPRD/HES-linked cohort study of people with bariatric surgery and the corresponding propensity score-matched* comparison cohort (data are n (%) unless otherwise specified)

Bariatric surgery
(n=2643)
Matched comparison group without surgery
(n=2595)
P values†
Follow-up (years), median (IQR)2.9 (3.2)2.9 (3.4)0.616
Age (years), mean (SD)45.2 (10.7)45.0 (10.8)0.417
 17–39, n (%)818 (31.0)826 (31.8)0.727
 40–49, n (%)945 (35.8)928 (35.8)
 50–85, n (%)880 (33.3)841 (32.4)
BMI at baseline, mean (SD)44.9 (8.9)42.2 (6.5)<0.001
 13–34, n (%)297 (11.2)287 (11.1)<0.001
 35–39, n (%)448 (17.0)456 (17.6)
 40–44, n (%)625 (23.7)1118 (43.1)
 45–49, n (%)571 (21.6)438 (16.9)
 50–94, n (%)667 (25.2)253 (9.8)
 Missing, n (%)35 (1.3)43 (1.7)
Female2131 (80.6)2131 (82.1)0.166
History of
Cerebrovascular disease37 (1.4)26 (1.0)0.186
Coronary heart disease104 (3.9)82 (3.2)0.130
Peripheral vascular disease11 (0.4)15 (0.6)0.405
Other atheroma0<5‡0.313
T2DM900 (34.1)853 (32.9)0.365
Taking oral antidiabetic571 (21.6)455 (17.5)<0.001
Taking insulin180 (6.8)156 (6.0)0.238
Hypertension890 (33.7)869 (33.5)0.886
Statin use699 (26.4)640 (24.7)0.139
AKI30 (1.1)11 (0.4)0.003
Alcohol status
 Non-drinker435 (16.5)397 (15.3)0.366
 Ex-drinker278 (10.5)236 (9.1)
 Current drinker (amount unknown)15 (0.6)13 (0.5)
 <2 units/day659 (24.9)644 (24.8)
 3–6 units/day862 (32.6)909 (35.0)
 >6 units/day170 (6.4)164 (6.3)
 Unknown224 (8.5)232 (8.9)
Smoking status
 Non-smoker1126 (42.6)1151 (44.4)0.093
 Current smoker403 (15.3)345 (13.3)
 Ex-smoker1112 (42.1)1099 (42.4)
 Unknown<5‡0
CKD at baseline
 Baseline CKD status absent1119 (42.3)1299 (50.1)<0.001
 No CKD1470 (55.6)1242 (47.9)
 Stage 3a27 (1.0)37 (1.4)
 Stage 3b16 (0.6)10 (0.4)
 Stage 410 (0.4)5 (0.2)
 Stage 5<5‡<5‡
Type of bariatric surgery
 Gastric band1193 (45.1)
 Sleeve gastrectomy364 (13.8)
 Gastric bypass1075 (40.7)
 Other11 (0.4)
ICD-10 code for AKI during follow-upn=44n=62
 N17.0 (acute kidney failure with tubular necrosis)<5‡<5‡0.927
 N17.9 (acute kidney failure, unspecified)38 (86.4)52 (83.9)
 N19 (unspecified kidney failure)5 (11.4)8 (12.9)
  • *In the original study, each surgery patient was matched 1:1 to the person without surgery with the closest propensity score, choosing matches at random where more than one possible match had the same score.7

  • †Categorical variables: χ2 test; continuous variables: Student’s t-test+SD if normally distributed, Wilcoxon rank-sum test+IQR if non-normally distributed.

  • ‡Cell counts <5 have been suppressed to ensure anonymity.

  • AKI, acute kidney injury; BMI, body mass index; CKD, chronic kidney disease; CPRD, Clinical Practice Research Datalink; HES, Hospital Episodes Statistics; ICD-10, International Classification of Diseases, 10th Revision; T2DM, type 2 diabetes mellitus.