Obesity, Underweight, and Accuracy of eGFR Using Cystatin C and Creatinine in a Northern European Population.
cross_sectional · Level IV
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- Record sourced from PubMed, PMID 40512561.
- Also identified by DOI 10.1681/ASN.0000000760 and PMC identifier 12591688.
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Abstract
Indexed eGFR<sub>cr-cys</sub> outperformed eGFR<sub>cr</sub> or eGFR<sub>cys</sub> across the body mass index (BMI) spectrum, improving GFR classification and treatment decisions. Nonindexed eGFR<sub>cr-cys</sub> led to further but smaller improvement across the BMI range that was not consistently related to BMI category. These findings inform clinical decisions on how to estimate GFR in the large segment of society living with low or high extremes of BMI. The presence of a low or high body mass index (BMI) in patients may influence the accuracy of eGFR. This study evaluates the performance of eGFR equations across the range of BMI. This is an observational study of 4707 adults (7503 repeated observations) referred for measured GFR (mGFR) in Stockholm, Sweden. We calculated indexed eGFR (in ml/min per 1.73 m<sup>2</sup>) and nonindexed eGFR (in ml/min) with validated equations that use creatinine (eGFR<sub>cr</sub>), cystatin C (eGFR<sub>cys</sub>), or both (eGFR<sub>cr-cys</sub>). We assessed equation performance against indexed and nonindexed mGFR across categories of BMI with median bias, <i>P</i><sub>30</sub> (the percentage of estimated values within 30% of mGFR), and classification of GFR categories, and modeled the implications of choice of filtration marker and indexing on clinical decisions regarding dose adjustment or eligibility for treatment. The mean age (SD) was 57 (16) years (39% female), and the median (interquartile range) indexed and nonindexed mGFR were 59 (39–79) and 65 (42–87) ml/min, respectively. In total, 9% of participants were underweight (BMI <20 kg/m<sup>2</sup>) and 18% were obese (BMI ≥30 kg/m<sup>2</sup>). For indexed and nonindexed eGFR for all equations, eGFR<sub>cr</sub> overestimated mGFR at BMI <20 and ≥30 kg/m<sup>2</sup>, and eGFR<sub>cys</sub> underestimated mGFR at BMI ≥30 kg/m<sup>2</sup>. eGFR<sub>cr-cys</sub> had the least bias, acceptable <i>P</i><sub>30</sub>, and the highest correct classification throughout the BMI range. In theoretical modeling, using indexed eGFR<sub>cr-cys</sub> versus eGFR<sub>cr</sub> would allow more accurate clinical decisions across all BMI categories. Using nonindexed versus indexed eGFR<sub>cr-cys</sub> led to further but smaller improvement that was not consistently related to BMI category for these decisions. In a clinic population of northern European individuals referred for GFR measurement, indexed eGFR<sub>cr-cys</sub> was more accurate than indexed eGFR<sub>cr</sub> across the BMI spectrum. Using nonindexed eGFR<sub>cr-cys</sub> further improved accuracy for some treatment decisions.