creatinine, cystatin C, or both, in NWB individuals and matched ambulatory controls. METHODS: Electronic medical records were reviewed for individuals with serum creatinine (Cr) and cystatin C (cys) and diagnosis consistent with NWB status, and ambulatory controls matched by age, race, sex, kidney function, diabetes, and hypertension. 2021 CKD-EPI race agnostic equations were used to calculate eGFR. Demographics and renal function were compared in the overall cohorts and in a patient subset with imaging and/or urinalysis evidence of renal dysfunction. Patients who were classified into a new eGFR category based on the incorporation of cystatin C were determined. eGFR classifications reflected those used in chronic kidney disease staging: CKD stage 1 !90 mL/min/1.73 m 2 , CKD stage 2 60-89 mL/min/1.73 m 2 , CKD stage 3 30-59 mL/min/1.73 m 2 , CKD stage 4 15-29 mL/min/1.73 m 2 , and CKD stage 5 <15 mL/min/1.73 m 2 .RESULTS: In the NWB population (n[102), eGFR differed significantly when calculated using CKD-EPI Cr , CKD-EPI CrþCys and CKD-EPI Cys (107, 93, 80 mL/min/1.73 m 2 , respectively, p<0.001). The differences in eGFR were greater in the NWB group relative to the control group (n[204) regardless of CKD-EPI equation pairs compared (p<0.001, Table 1). In the patient subset with imaging and/or proteinuria evidence of renal dysfunction, the NWB population again had different eGFR when calculated using the CKD-EPI Cr , CKD-EPI CrþCys and CKD-EPI Cys equations (102, 86, 71 mL/min/1.73 m 2 , respectively, p<0.001). Fifty-eight percent of NWB individuals with evidence of renal dysfunction on imaging or urinalysis were reclassified into a category of lower eGFR (corresponding to CKD stage) when using eGFR Cys relative to eGFR Cr .CONCLUSIONS: eGFR equations containing serum creatinine, cystatin C, or both, validated in mostly ambulatory populations, are not equivalently accurate in estimating kidney function in NWB individuals. Comparison of these equations against gold standard GFR measurement is needed to determine which most closely approximates true GFR.
