#1128 Accuracy of shorter iohexol glomerular filtration rate measurement protocols in individuals with preserved kidney function

Abstract

Abstract Background and Aims Measuring glomerular filtration rate (mGFR) using exogenous tracers is recommended in a number of settings with plasma one-compartment multi-sample protocols (MSP) being the most commonly used and iohexol being the dominant tracer. The accuracy of MSP protocols has mostly been evaluated in the setting of reduced GFR where delayed initial and final samples are recommended. Much less is known about MSPs when GFR is not decreased and the default protocol tends to include initial sampling at 120 minutes and final sampling at 240 minutes post iohexol injection. The objective of this study was to assess the performance of shorter MSPs with earlier initial (60 and 90 minutes) and final (150, 180, and 210 minutes) sampling times in individuals with preserved GFR. Method Participants were recruited from a 4-year prospective, observational study evaluating the cardiovascular, renal, and bone health profile of young adults with Type 1 Diabetes. The reference mGFR was calculated using a plasma iohexol clearance one compartment slope intercept method with 5 samples collected between 120-240 minutes post iohexol injection. Four different combinations of shorter sampling strategies were investigated: 60-150 min, 60-180 min, 90-180 min and 90-210 min. Performance was evaluated using measurements of bias, precision, and accuracy (P2, P5, and mean absolute error). Results Mean age of the 43 participants was 23.9 ± 1.9 yrs with a mean eGFRCKiD-1 of 95.5 ± 15.9 ml/min/1.73 m2 and mean reference mGFR (120-240 min) of 102.3 ± 13.7 ml/min/1.73 m2. All exploratory shorter mGFRs performed well, with median biases less than 1 ml/min/1.73 m2 and mean absolute error less than 1.6 ml/min/1.73 m2. All shorter mGFRs were within 5% of the reference mGFR and the majority were within 2%. Conclusion These results demonstrate that shortening the mGFR procedure in individuals with preserved GFR provided very similar results to the current standard while significantly decreasing procedure time. The cost savings and improved feasibility of these shortened protocols should reduce some of the barriers to more widespread adoption of GFR measurement.