Estimated Glomerular Filtration Rate Bias in Participants with Severe Obesity Regardless of Deindexation

Abstract

Objective Morbid obesity is associated with a higher independent risk of chronic kidney disease (CKD). Estimated glomerular filtration rate (eGFR) has been evaluated in a limited number of study participants with severe obesity. Methods A total of 706 measured GFR (mGFR) results from 598 participants with obesity (BMI ≥ 35 kg/m2) were retrospectively collected. The performance of the Modification of Diet in Renal Disease (MDRD) equation, Chronic Kidney Disease‐Epidemiology (CKD‐EPI) equation, and deindexed eGFR were compared with mGFR from the gold standard technique (inuline or iohexol), adjusted (mGFRr) or nonadjusted (mGFR) to body surface area. Absolute bias, precision, and accuracy were calculated. Results Mean mGFRr (58 ± 31 mL/min/1.73 m2) was significantly different from CKD‐EPI and MDRD (P < 0.001). Mean mGFR (nonindexed) (70 ± 40 mL/min) was significantly higher than mGFRr (P < 0.001). eGFR showed important biases and low accuracies for CKD‐EPI and MDRD (10.7 ± 10.7 and 12.2 ± 13.7 mL/min/1.73 m2; 78% vs. 75% respectively). Deindexation worsened bias and accuracy 30% (percentage of GFR estimates within 30% of mGFRr or mGFR) between eGFR and mGFR. Conclusions eGFR overestimates mGFR and is associated with important biases and inaccuracies in patients with severe obesity, and deindexing eGFR worsens the overestimation. These findings may have important implications in examining kidney function in patients with obesity.

The Enlarging Effect of Obesity on Estimating Kidney Function: Blaming Serum Creatinine Versus Indexation and Methodology

“…The authors concluded that the BSA‐indexed eGFR, regardless of the use of CKD‐EPI or MDRD equations, tends to overestimate kidney function in morbid obesity. Deindexation did not remedy the biases and inaccuracies of eGFR and indeed worsened the overestimation according to the authors .…”

“…Similarly, fasting for Ramadhan increased the eGFR likely because of loss of muscle and/or reduction of dietary meat intake . Notwithstanding these data, it is not clear why the eGFR overestimated the mGFR in morbid obesity in the study by Guebre‐Egziabher et al . However, the removal of indexation for BSA did not improve the estimate but worsened it.…”

“…This approach may lead to erroneously skewed values in persons with morbid obesity, in whom the BSA‐indexed eGFR can be misleading relative to the underlying raw GFR values as a result of distortion by a rather large BSA in the denominator. In a landmark study by Guebre‐Egziabher et al in this issue of Obesity , the GFR was laboriously measured (mGFR) by either inulin or iohexol, as the gold standards, in 706 adults with morbid obesity and BMI > 35 kg/m 2 . The investigators found that the eGFR, using the commonly employed Chronic Kidney Disease‐Epidemiology (CDK‐EPI) Collaboration and Modification of Diet in Renal Disease (MDRD) equations, overestimated the mGFR that was indexed for BSA; the median values were 56 (CKD‐EPI equation eGFR) and 55 (MDRD equation eGFR) versus 50 mL/min/1.73 m 2 BSA (mGFR).…”

Assessment of Kidney Function in Patients With Extreme Obesity: A Narrative Review

“…The second large study was a retrospective evaluation comparing the performance of MDRD4 and CKD-EPI equations with inulin or iohexol in 598 patients with various nephropathies and BMIs ≥35 kg/m 2 (mean 39.6 ± 4.3 kg/ m 2 ). 36 [47 to 54] mL/min/1.73 m 2 , respectively; P < 0.01 for both), with deindexing increasing the overestimation (data not shown). These 2 studies evaluating the performance of MDRD4 and CKD-EPI in patients with obesity indicate significant biases and inaccuracies compared with mGFR.…”

“…The second large study was a retrospective evaluation comparing the performance of MDRD4 and CKD-EPI equations with inulin or iohexol in 598 patients with various nephropathies and BMIs ≥35 kg/m 2 (mean 39.6 ± 4.3 kg/m 2 ). 36 The median absolute bias (99.6% CI) was significantly greater for MDRD4 compared with CKD-EPI (8.0 [6.8-9.6] vs 7.3 [6.4-8.6], respectively; P < 0.05) and accuracy defined as within 30% of mGFR was significantly less with MDRD4 (75 [69-79] vs 78 [73-83], respectively; P < 0.05). However, both the MDRD4 and CKD-EPI equations significantly overestimated mGFR (median [95% CI], 55 [53-59] mL/min/1.73 m 2 and 56 [53-58] mL/min/1.73 m 2 vs 50 [47 to 54] mL/min/1.73 m 2 , respectively; P < 0.01 for both), with deindexing increasing the overestimation (data not shown).…”