Accuracy of Glomerular Filtration Rate Estimates among Patients with Cancer

Background: Little is known about the accuracy of glomerular filtration rate (GFR) assessment among people with cancer. Most cancer guidelines and trials recommend estimated creatinine clearance (eClcr) using the Cockcroft-Gault (CG) equation. Accuracy is key to determine cancer prognosis, treatment eligibility and correct dosing of treatments with narrow therapeutic index. Methods: We performed a cross-sectional study including 1,781 adults with incident cancer referred for 1,989 determinations of measured GFR (mGFR) using single-point plasma clearance of iohexol in Stockholm, Sweden, with concurrent measurements of creatinine and cystatin C. We assessed the performance of eClcr, estimated GFR based on creatinine (eGFRcr: CKD-EPI 2009/2021, EKFC 2021), cystatin C (eGFRcys: CKD-EPI 2012, EKFC 2023) and the combination (eGFRcr-cys: CKD-EPI 2012/2021, EKFC 2023) equations against mGFR. Values were non-indexed to body surface area and reported in mL/min. Accuracy was reported as % of patients with estimated values that differed by more than 30% of mGFR (1-P30). Bias was estimated as median (interquartile range; IQR) difference between mGFR and eCrcl or eGFR. Results: Mean age was 64 (SD 14) years, 36% were female with mean mGFR 76 (SD 31) mL/min. The most common cancers were bladder (41%), lung (15%) and colorectal (13%); 13% had metastatic disease. 1-P30 was best for eGFRcr-cys (6-8%). eClcr (1-P30: 17%) had similar accuracy to eGFRcr (1-P30: 13-26%) and eGFRcys (1-P30: 12-17%). Accuracy varied by mGFR (Figure A). Median bias was lowest for eGFRcr-cys CKD-EPI 2012 (-0.5, IQR -6.2 to 6.4 mL/min) and highest for eGFRcr CKD-EPI 2021 (9.8, IQR 0.9 to 19.7 mL/min). Across mGFR categories, eGFRcr-cys equations were the least biased (Figure B). Conclusion: Non-indexed eGFRcr-cys with CKD-EPI and EKFC equations provide the most accurate estimates of mGFR in patients with cancer, with potential to improve dosing and classification across treatment thresholds compared to eClcr and eGFRcr.