#444 Novel MRI filtration fraction method to assess glomerular hemodynamics in diabetic kidney disease

Abstract

Abstract Background and Aims Filtration fraction (FF) is the ratio of the glomerular filtration rate (GFR) to renal plasma flow (RPF) and is therefore an important measure of glomerular hemodynamics. The gold standard method to assess effective RPF is renal clearance of para-aminohippuric acid (PAH) but technical and labour-intensive difficulties limit its application [1]. Quicker and simpler assays of FF are needed, particularly to assess the renal hemodynamic dysfunction (hyper- or hypofiltration) and effects/mode of action of therapeutic interventions in chronic kidney disease (CKD). We assessed a novel magnetic resonance imaging (MRI) technique to measure FF in patients with diabetic kidney disease (DKD) and healthy controls (HC) [2]. Method This cross-sectional sub-study included 32 DKD subjects with measured GFR (mGFR) ≤ 60 ml/ min/1.73 m2 and stratified into the following GFR stages as per the Kidney Disease Improving Global Outcomes (KDIGO) classification: stage G3a (mGFR 45-59 ml/ min/1.73 m2, n = 3), G3b (mGFR 30-44 ml/ min/1.73 m2, n = 8), G4 (mGFR 15-29 ml/ min/1.73 m2, n = 15), G5 (<15 ml/ min/1.73 m2, n = 6), and 18 age-, gender-matched HC with mGFR ≥ 60 ml/min/1.73 m2. All subjects were 18-79 years old. mGFR was assessed using iohexol clearance. Renal blood flow (RBF) (ml/min) was measured by a 5-minute add-on phase contrast MRI of the renal artery of each kidney and then summed together. RBF was corrected for Body Surface Area. RPF and FF were calculated as below: ${\rm{RPF }} = {\rm{ RBF}} \times \ ( {1\ -{\rm{ Hematocrit}}} )$ ${\rm{FF}} = {\rm{mGFR}}/{\rm{RPF}}$ Results RBF and mGFR were highly correlated (R2 = 0.70, Fig. 1). FF was 17.1% for HC and decreased with increasing degrees of renal impairment (Fig. 2). While the difference between HC and G3a DKD group was not significant, there was highly significant difference between HC and all other DKD groups (p < 0.001). The standard deviation in the G3a group was relatively large with only 3 subjects in this group. Conclusion The phase contrast MRI scan can provide a quick and simple measurement of glomerular hemodynamics and therewith further insights into the pathophysiology of DKD and its progression. Given the limitations of the existing method for assessing renal plasma flow, this MRI method can facilitate the inclusion of filtration fraction in DKD clinical trials. Further, the described method could be used to identify hyperfiltration, a compensatory mechanism that can influence results in clinical trials of DKD.