Estimating Changes in Glomerular Filtration Rate With Fluorescein Isothiocyanate-Sinistrin During Renal Replacement Therapy

Excreted exclusively by the kidneys, fluorescein isothiocyanate (FITC)-sinistrin can be used to measure glomerular filtration rate (GFR) and is detectable transdermally. Determination of changes in native kidney GFR (NK-GFR) in patients with acute kidney injury, particularly during continuous renal replacement therapy, improves clinical decision-making capability. To test feasibility of measuring changes in NK-GFR during CRRT with FITC-sinistrin, in vitro circuits (n = 2) were utilized to simultaneously clear FITC-sinistrin by removal of ultrafiltrate at varying rates, simulating kidney function, and by dialysis at a constant rate. Clearance calculated by fluorescence-measuring devices on the circuit showed good agreement with clearance calculated from assay of fluid samples ( R2 = 0.949). In vivo feasibility was studied by dialyzing anesthetized pigs (n = 3) and measuring FITC-sinistrin clearance during progression from normal, to unilaterally, then bilaterally nephrectomized. FITC-sinistrin clearance was reduced in vitro , when ultrafiltrate was decreased or with successive nephrectomies in vivo . Transdermal readers showed 100% sensitivity in detecting a decrease in NK-GFR in pigs with a bias of 6.5 ± 13.4% between transdermal-derived GFR (tGFR) and plasma-measured methods determining proportional changes in clearance. Clearance of FITC-sinistrin by dialysis remained consistent. In patients receiving a constant dialysis prescription, transdermal measurement of FITC-sinistrin can detect relative changes in NK-GFR.