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Performance of Glomerular Filtration Rate Estimating Equations Before and After Bariatric Surgery.


ABSTRACT:

Rationale & objective

Evaluation of glomerular filtration rate (GFR) is challenging in adults undergoing bariatric surgery because creatinine and cystatin C levels are influenced by changes in muscle and fat mass. Additionally, indexing of GFR by body surface area (BSA) may by affected by decreases in BSA.

Study design

Prospective observational study.

Setting & participants

27 adults with body mass index (BMI) ? 35 kg/m2 who underwent measurement of GFR before and after bariatric surgery.

Outcomes

Indexed and nonindexed GFRs measured (mGFRs) using plasma iohexol clearance, indexed and nonindexed estimated GFR (eGFR) based on levels of creatinine, cystatin C, or both from Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations.

Analytic approach

Bias and percent of estimates within 20% and 30% of mGFR (P20 and P30) for estimating equations were examined.

Results

Mean presurgery BMI was 49.5 (SD, 9.4) kg/m2, BSA was 2.42 (SD, 0.27) m2, nonindexed mGFR was 117.3 (SD, 34.1) mL/min, and indexed mGFR was 84.1 (SD, 22.0) mL/min/1.73 m2. After 6 months, mean BMI changed by -13.8 (95% CI, -15.9 to -11.8) kg/m2, BSA by -0.30 (95% CI, -0.33 to -0.27) m2, and nonindexed mGFR by -9.2 (95% CI, -17.2 to -1.1) mL/min, while indexed mGFR was unchanged at 5.1 (95% CI, -0.1 to 10.4) mL/min/1.73 m2. Nonindexed eGFRcr was unbiased (median bias, 5.0 [95% CI, -4.3 to 11.6] mL/min) before surgery, but overestimated mGFR (8.8 [95% CI, 1.8 to 16.9] mL/min) after surgery. Nonindexed eGFRcys underestimated mGFR before (median bias, -12.1 [95% CI, -21.4 to -1.2] mL/min) and after surgery (-11.2 [95% CI, -21.8 to -7.3] mL/min). Nonindexed eGFRcr-cys was unbiased before (median bias, -6.0 [95% CI, -11.0 to 1.0] mL/min) and after surgery (-2.0 [95% CI, -8.8 to 4.9] mL/min). Findings were similar for indexed eGFR compared with indexed mGFR.

Limitations

Small, mostly white sample.

Conclusions

Changes in indexed and nonindexed GFRs may be discordant after bariatric surgery in adults because of decreases in BSA. Indexed and nonindexed eGFRcr-cys may be less biased than indexed or nonindexed eGFRcr or eGFRcys because of opposite biases in estimating mGFR.

SUBMITTER: Chang AR 

PROVIDER: S-EPMC7729215 | BioStudies | 2020-01-01

REPOSITORIES: biostudies

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