Development and validation of a new equation based on plasma creatinine and muscle mass assessed by CT-scan to estimate glomerular filtration rate: a cross-sectional study

Abstract Background Inter-individual variations of non-GFR determinants of serum creatinine, such as muscle mass, account for the imperfect performance of eGFR equations. We aimed to develop an equation based on creatinine and total lumbar muscle cross-sectional area (MCSA) measured by unenhanced CT-scan at the third lumbar vertebra. Methods The muscle mass-based eGFR (MMB-eGFR) equation was developed in 118 kidney donor candidates (iohexol clearance) using linear regression. Validation cohorts included 114 healthy subjects from another center (51Cr-EDTA clearance, validation population-1), 55 patients with chronic diseases (iohexol, validation population-2), and 60 patients with highly discordant creatinine and cystatin C-based eGFR, thus presumed to have atypical non-GFR determinants of creatinine (51Cr-EDTA, validation population-3). Mean bias was the mean difference between eGFR and mGFR, precision the standard deviation of the bias, and accuracy the percentage of eGFR values falling within 20 and 30% of mGFR. Results In validation population-1, performance of MMB-eGFR was not different from those of CKD-EPICr2009 and CKD-EPICr2021. In validation population-2, MMB-eGFR was unbiased and displayed better precision than CKD-EPICr2009, CKD-EPICr2021, and EKFC (SD of the biases: 13.1 vs 16.5, 16.8 and 15.9 ml/min/1.73m2). In validation population-3, MMB-eGFR had better precision and accuracy (accuracy within 30%: 75.0% (95%CI 64.0–86.0) vs 51.5% (95%CI 39.0–64.3) for CKD-EPICr2009, 43.3% (95%CI 31.0–55.9) and 53.3% (95%CI 40.7- 66.0) for EKFC). Difference in bias between black and white subjects was −2.1 ml/min/1.73m2 (95%CI: −7.2;3.0), vs −8.4 ml/min/1.73m2 (95%CI: −13.2; −3.6) for CKD-EPICr2021. Conclusion MMB-eGFR displayed better performances than equations based on demographics, and could be applied to subjects of various ethnic backgrounds.