Estimation of glomerular filtration rate by standard renal CT imaging.

OBJECTIVES: To develop and evaluate a method to predict glomerular filtration rate (GFR) from clinical renal CT. MATERIALS AND METHODS: Medical records of adult living kidney donors operated between 2013 and 2022 and patients considered for neoadjuvant cisplatin prior to cystectomy between 2019 and 2024 were retrospectively reviewed. Inclusion criteria were (1) renal CT obtained at 100 or 120 kVp before and 5-15 min after contrast administration, and (2) iohexol clearance test within 2 months of imaging. The iohexol clearance test was performed on the same day as the cystatin C and creatinine measurements. Estimated GFR values included cystatin C-based eGFR (eGFRcystatin C), creatinine-based eGFR using the Cockcroft-Gault formula (eGFRCockcroft-Gault), and eGFR using the Revised Lund-Malmö formula (eGFRLMR18), which is based on both creatinine and cystatin C. Manual and automatic segmentations of the renal pelvis and bladder were performed in both the excretory and unenhanced phases. RESULTS: In total, 139 patients were included in the analysis (mean age 52 ± 13 years; 60% women). Multivariate linear regression analysis combining the segmentation-derived variable with body surface area and age gave an adjusted R-square of 0.77 to mGFRiohexol (p < 0.001). GFRCT had the strongest relationship to mGFRiohexol with a mean absolute error of 12.8 mL/min, compared with 15.6 mL/min for eGFRCockcroft-Gault, 14.2 mL/min for eGFRcystatin C, and 13.0 mL/min for eGFRLMR18. Manual and automatic segmentations had similar performance. Patients evaluated for cisplatin treatment had greater variation in CT-estimated split renal function than donors. CONCLUSION: Renal function can be estimated with high precision from clinical renal CT. KEY POINTS: Question Accurate GFR assessment is critical, but current methods are either labor-intensive or imprecise. Can renal CT imaging provide a reliable alternative? Findings CT-derived eGFR showed the strongest correlation with iohexol clearance (R² = 0.77), with lower error compared to creatinine- and cystatin C-based estimates. Critical relevance statement Routine CT imaging can provide precise estimates of kidney function, supporting donor evaluations, chemotherapy dosing, and critical care decisions when accurate renal function is essential.