Model‐Derived Iopamidol Clearance and Creatinine‐Based Kidney Function Estimates After Trauma: A Retrospective Cohort Study

Study Objective To determine whether iopamidol administered during clinically indicated contrast‐enhanced computed tomography (CE‐CT) and measured in remnant serum can provide an individualized surrogate value for measured glomerular filtration rate (mGFR) after trauma to compare against creatinine‐based estimates. Design Single‐center retrospective observational cohort. Setting Academic medical center. Patients Seventy‐six adults evaluated for trauma who underwent iopamidol‐enhanced CT and had at least one quantifiable postcontrast concentration and serum creatinine measurement. Intervention None. Measurements and Main Results Population parameters of a previously developed two‐compartment structural model were re‐estimated using the study data and stochastic approximation expectation–maximization, followed by participant‐specific conditional‐mode clearance estimation. Individual iopamidol clearance was interpreted as mGFR (mGFR IOP ). Agreement with Cockcroft–Gault creatinine clearance and nonindexed Chronic Kidney Disease Epidemiology Collaboration (CKD‐EPI) creatinine estimated GFR was assessed; 449 serum creatinine measurements were modeled over 7 days. Median mGFR IOP was 99 mL/min (interquartile range, 59–125). Each 30‐mL/min higher mGFR IOP was associated with a 0.11‐mg/dL lower serum creatinine at iopamidol administration (95% confidence interval, 0.06–0.16; p < 0.001). Predicted serum creatinine values converged over 7 days despite differences in mGFR IOP (interaction p < 0.001). Estimates were within 30% of mGFR IOP in 71% of patients for CKD‐EPI versus 59% for Cockcroft–Gault ( p = 0.035). CKD‐EPI had narrower 95% limits of agreement compared with Cockcroft‐Gault (−73 to 57 vs. −82 to 74 mL/min, respectively) but increasingly underestimated higher mGFR IOP (proportional‐bias p < 0.001). Conclusion Cohort‐specific iopamidol clearance estimates as a surrogate for mGFR can be generated from routine CE‐CT and remnant serum samples that differ from creatinine‐based estimates. Prospective validation against conventional mGFR is required before clinical use.