Table 2.

Association of bariatric surgery with first incident AKI, stratified by length of follow-up

	PY	Events	Rate per 1000 PY (95% CI)	Crude RR (95% CI)*	P values†	Adjusted RR (95% CI)‡	P values†
All patients
Day 1–30
Unexposed	203	0	0	–
Bariatric surgery	199	5	25.1 (10.5 to 60.4)	–
>Day 30
Unexposed	7882	54	6.9 (5.2 to 8.9)	–
Bariatric surgery	8061	34	4.2 (3.0 to 5.9)	0.62 (0.40 to 0.95)	0.027	0.37 (0.23 to 0.61)	<0.001
All patients analysed by type of surgery§
Day 1–30
Unexposed
Gastric band
Sleeve gastrectomy
Gastric bypass
Other
>Day 30
Unexposed	7882	54	6.9 (5.2 to 8.9)	–
Gastric band	4614	17	3.7 (2.3 to 5.9)	0.54 (0.31 to 0.93)	0.026
Sleeve gastrectomy	728	<5¶	5.5 (2.1 to 14.6)	0.80 (0.29 to 2.21)	0.670
Gastric bypass	2655	13	4.9 (2.8 to 8.4)	0.71 (0.39 to 1.31)	0.277
Other	63	0	–	–
All patients over whole period of follow-up
Unexposed	8085	54	6.7 (5.1 to 8.7)	–
Bariatric surgery	8259	39	4.7 (3.5 to 6.5)	0.71 (0.47 to 1.07)	0.099	0.45 (0.28 to 0.72)	0.001

Unexposed refers to the propensity-matched comparison group.

*Poisson regression model.

†Wald test.

‡Poisson regression model adjusted for age at baseline, sex, calendar time, CKD at baseline, history of AKI, history of taking oral antidiabetics and BMI at baseline.

§No analysis for day 1–30 owing to sparse data.

¶Cell counts <5 have been suppressed to ensure anonymity.

AKI, acute kidney injury; BMI, body mass index; CKD, chronic kidney disease; PY, person years; RR, rate ratio.