MBS patients faced increased risk of acute kidney injury and ten-year risk of nephrolithiasis

A population-based study comparing patients undergoing bariatric surgery with patients diagnosed with obesity/overweight, has found surgery patients had an increased one-year risk of acute kidney injury (AKI) and ten-year risk of nephrolithiasis, but a decreased ten-year risks of chronic kidney disease (CKD) (G3-5) and kidney failure with replacement therapy (KFRT), according to researchers from Aarhus University and Aarhus University Hospital, Denmark.

Using data from the Danish National Patient Registry, the study included 18,827 individuals in the bariatric surgery cohort (17,200 with RYGB and 1,627 with SG) and 94,135 individuals in each of the overweight/obesity and population comparison cohorts. The median follow-up time was 8.1 years (IQR: 5.2; 9.2) in the bariatric surgery cohort, 7.9 years (IQR: 4.2; 9.1) in the overweight/obesity cohort, and 8.0 years (IQR: 4.6; 9.1) in the population cohort. For the RYGB and SG cohorts, it was 8.2 years (IQR: 6.3; 9.3) and 1.8 years (IQR: 0.8; 3.0), respectively. The median age was 41 years (IQR: 34; 48), and 76% were female.

The median eGFR was 103 ml/min/1.73 m2 (IQR: 91; 113) for the bariatric surgery cohort and 103 ml/min/1.73 m2 (IQR: 91; 112) for the overweight/obesity cohort. Median baseline HbA1c was also comparable with 36 mmol/mol in the bariatric surgery cohort and 38 mmol/mol in the overweight/obesity cohort. In the bariatric surgery cohort, 4.6% had a CCI score ≥3 compared to 7.4% in the overweight/obesity cohort. Hypertension was observed in 22% of the bariatric surgery cohort and 19% of the overweight/obesity cohort, while diabetes was present in 20% and 17% of the cohorts, respectively. In general, the population cohort had a lower level of comorbidities compared with the overweight/obesity comparison cohort.

Subcohorts with available eGFR at index included 8,973 bariatric surgery patients (7,542 with RYGB and 1,431 with SG), and 18,498 matched overweight/obesity comparisons.

Outcomes

The one-year risk of AKI was 2.7% within the bariatric surgery cohort (2.7% and 2.4% in patients undergoing RYGB and SG, respectively). In comparison, the risk was 2.5% within the overweight/obesity comparison cohort and 1.1% within the population comparison cohort. The aHR for AKI was 1.63 (95% CI; 1.38, 1.92) when comparing the bariatric surgery cohort with the overweight/obesity cohort. For the RYGB cohort, the aHR was 1.64 (95% CI; 1.38, 1.94), and for the SG cohort, the aHR was 1.68 (95% CI; 1.16, 2.43). Compared with the population cohort, the aHR for AKI was even higher (Figure 1).

The ten-year risk of incident nephrolithiasis in the bariatric surgery cohort was 3.5% (3.6% and 1.2% in the RYGB and SG cohorts, respectively). In comparison, the risk was 2.4% in the overweight/obesity cohort and 1.3% in the population cohort.

The ten-year aHR for nephrolithiasis was 1.73 (95% CI; 1.56, 1.91) when comparing the bariatric surgery cohort with the overweight/obesity cohort. The corresponding aHR was 1.74 (95% CI; 1.58, 1.93) in the RYGB cohort and 1.33 (95% CI; 0.73, 2.40) in the SG cohort. The increased rates of nephrolithiasis following bariatric surgery were even more pronounced when compared with the population cohort.

The ten-year risk of incident CKD (stage G3–G5) was examined in patients with available eGFR at index. The risk was 0.4% in the bariatric surgery cohort (0.4% and 0.0% in the RYGB and SG cohorts, respectively). In comparison, the risk was 1.7% in the overweight/obesity cohort and 0.6% in the population cohort. When comparing the bariatric surgery cohort with the overweight/obesity cohort the aHR was reduced at 0.41 (95% CI; 0.26, 0.66). The aHR was 0.43 (95% CI; 0.26, 0.69) in the RYGB cohort and could not be calculated for the SG cohort because of no CKD events. Reduced rates of CKD after bariatric surgery were also observed when compared with the population cohort.

The 10-year risk of incident KFRT was 0.2% in the bariatric surgery cohort (0.2% and 1.6% in the RYGB and SG cohorts, respectively). In comparison, the risk was 0.4% in the overweight/obesity cohort and 0.1% in the population cohort. The ten-year aHR was 0.63 (95% CI; 0.42, 0.95) when comparing the bariatric surgery cohort with the overweight/obesity cohort. The aHR was 0.57 (95% CI; 0.37, 0.88) in the RYGB cohort and 2.55 (95% CI; 0.81, 8.00) in the SG cohort. When comparing the bariatric surgery cohort with the population cohort, the aHR for KFRT was also decreased.

“Collectively, these findings support the need to address and manage the initial post-operative risk of AKI and the long-term risk of nephrolithiasis in patients undergoing bariatric surgery,” the authors concluded.

The findings were featured in the paper, 'Kidney outcomes after bariatric surgery: a population-based cohort study', published in BMC Nephrology. To access this paper, please click here