We are aware of the ongoing discussions of GFR normalization to body weight. Our system detects the decrease of fluorescence of FITC-Sinistrin in the extracellular space. Thus, increased fat content does not influence the measurement (no lipid binding has been reported for FITC-Sinistrin). Many researchers have used our tGFR System in obese animals (please see the list of publications on our website).
Regarding normalization to bodyweight it has been reported that GFR/bodyweight declines after a certain bodyweight. However, this is due to the normalization itself rather than to an actual decline in function. Also, this decline is seen in GFR regardless of the technique you choose for GFR measurement.1 Therefore, our advice is to evaluate both normalized as well as absolute GFR independently in your publication/research.