Continuous Infusion of Low-Dose Iohexol Measures Changing Glomerular Filtration Rate in Critically Ill Patients

OBJECTIVE: Measurement of changing glomerular filtration rate in acute kidney injury remains problematic. We have previously used a continuous infusion of low-dose Iohexol to measure glomerular filtration rate in stable subjects and postulate that changes greater than 10.3% in critically ill patients indicate acute kidney injury. Our objective is to explore the extent to which continuous infusion of low-dose Iohexol can be a measure of changing glomerular filtration rate during acute kidney injury. DESIGN: Clinical observational exploratory study. SETTING: Adult ICU. PATIENTS: Three patient groups were recruited: nephrectomy group: predictable onset of acute kidney injury and outcome (n = 10); surgery group: predictable onset of acute kidney injury, unpredictable outcome (n = 11); and acute kidney injury group: unpredictable onset of acute kidney injury and outcome (n = 13). INTERVENTIONS: Continuous infusion of low-dose Iohexol was administered for 24-80 hours. Plasma (ClP) and renal (ClR) Iohexol clearances were measured at timed intervals. MEASUREMENTS AND MAIN RESULTS: Kidney Disease: Improved Global Outcomes acute kidney injury criteria were fulfilled in 22 patients (nephrectomy = 5, surgery = 4, and acute kidney injury = 13); continuous infusion of low-dose Iohexol demonstrated acute kidney injury in 29 patients (nephrectomy = 10, surgery = 8, acute kidney injury = 11). Dynamic changes in glomerular filtration rate were tracked in all patients. In the nephrectomy group, ClR decreased by an expected 50% (50.8% ± 11.0%). Agreement between ClP and ClR improved with increasing duration of infusion: bias of ClP versus ClR at 48 hours was -0.1 ± 3.6 mL/min/1.73 m (limits of agreement: -7.2 to 7.1 mL/min/1.73 m). Coefficient of variation of laboratory sample analysis was 2.4%. CONCLUSIONS: Continuous infusion of low-dose Iohexol is accurate and precise when measuring glomerular filtration rate and tracks changes in patients with differing risks of acute kidney injury. Continuous infusion of low-dose Iohexol may provide a useful standard against which to test novel biomarkers for the diagnosis of acute kidney injury.