*Purpose: Progressive GFR decline post kidney transplantation is a general problem that requires accurate assessment of GFR for clinical decision making. The gold-standard radiotracer determined GFR (mGFR) is not easily accessible establishing the need for better GFR estimating methods. Limitations inherent in the CKD-EPI₂₀₁₂, creatinine-based equation are well established, and the inclusion of race potentially allows for their to be biases and disparity in management. Two new multi-parametric GFR estimating formulas have recently been established that eliminate race and include Cystatin-C and Creatinine for GFR estimation, CKD-EPI₂₀₂₁ and GFR_NMR. Although similar, NMR methodology permitting simultaneous measurement of multiple biomarkers expands on CKD-EPI₂₀₂₁ by the addition of myo-inositol and valine.

*Methods: In this study, we compared the performance of these GFR estimating equations to mGFR in post kidney transplant (n=220).

*Results: The p15 values of both CKD-EPI₂₀₂₁ (p15=60) and GFR_NMR (p15=67.73) show improved accuracy across the GFR range compared to CKD-EPI₂₀₁₂ (p=50.5) reflecting the benefit of a multi-biomarker assay. Importantly, both the newer GFR estimating equations performed well in patients with reduced kidney function (mGFR<60). GFR_NMR (p15=61.3) and CKD-EPI₂₀₂₁ (p15=60.5) were significantly more accurate than CKD-EPI₂₀₁₂ (p15=49.6). Further subgroup analysis also demonstrated the superiority of CKD-EPI₂₀₂₁ and GFR_NMR in both the elderly (Age>65) and the overweight (BMI>25). Importantly, these newer equations remove race from GFR estimating equations reducing the potential for bias.

*Conclusions: This study demonstrates that newer GFR estimating equations may be useful alternatives to mGFR in assessing kidney function post-transplantation. Further prospective studies with serial measurement using these GFR estimating equations will be necessary to determine their accuracy for assessing long-term kidney function in renal transplant.

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