#5993 Kinetics in Renal Functional Reserve Using Dtpa-Clearance Measurements

Abstract

Background and Aims Kidneys have an intrinsic reserve capacity to respond to a higher workload by increasing filtration in their nephrons, called renal functional reserve (RFR). Despite the high clinical relevance of RFR, the necessary dynamic measurements are rarely done in the clinical routine, due to time- and workload as well as lack of standardized protocols. Method We developed a novel RFR protocol using 99mTc-DTPA (DTPA-Cl) before and after an oral protein load performed in an outpatient clinical setting within one day. Following a weak of low protein diet and using standardized hydration baseline and post-stimulation GFR were measured. 50 MBq activity were given i.v. at 0 and 240 mins, the plasma clearance was calculated based on the activity course at 13 time-points over 480 mins. RFR was expressed as the difference of post-protein stimulation peak mGFR to baseline mGFR in fasting state. Results In the pilot study we measured RFR in 7 healthy participants. The results showed a high heterogeneity. Therefore, we modified the study protocol for the next 16 patients by (a) extending the time of measurements to 330 min post-stimulation and (b) increasing the frequency of activity measurements to every 30 mins. In addition, we used a protein load of 1.5 g/kg bwt of beef protein. These standardized measurements showed inter-individual time differences in reaching the peak GFR values post-protein load, the peaks detectable between 150 to 270 mins after the protein meal. The mean RFR (±SD) was 14 (±13) ml/min/1.73 m2 corresponding to 16 (±15)% [Fig. 1]. All participants demonstrated a significant fall in DTPA-Cl 60 mins post-stimulation. Conclusion RFR can be measured with a same day pre- and post-stimulation DTPA-clearance protocol. Using a high oral load of beef protein and a long, post-stimulation period of measurements demonstrates inter-individual differences in reaching the hyperfiltration peak and a significant, previously not appreciated, post-prandial drop in GFR.