Accuracy of Shorter Iohexol GFR Measurement Protocols in Individuals with Preserved Kidney Function.

Key Points: Shorter measured GFR protocols are accurate and precise compared with the reference standard measured GFR protocol in patients with preserved GFR. These shorter protocols can potentially improve the adoption of GFR measurement more widely by reducing procedural time and cost.

Background: Measured GFR (mGFR) using exogenous tracers is recommended in a number of settings. Plasma one-compartment multisample protocols (MSPs) are the most commonly used, with iohexol being the dominant tracer. The accuracy of MSPs 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 after iohexol injection. The recent Kidney Disease Improving Global Outcomes 2024 Clinical Practice Guideline for the Evaluation and Management of CKD includes research recommendations for the development of shorter more efficient mGFR protocols. 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. Reference mGFR (R-mGFR) was calculated using five samples collected between 120 and 240 minutes.

Methods: Four different combinations of shorter sampling strategies were investigated. Performance was evaluated using measurements of bias, precision, and accuracy (P2, P5, and mean absolute error).

Results: The mean R-mGFR of the 43 participants was 102.3±13.7 ml/min per 1.73 m. All shorter mGFRs had biases <1 ml/min per 1.73 m and mean absolute error <1.6 ml/min per 1.73 m. All shorter mGFRs were within 5% of the R-mGFR, and the majority were within 2%.

Conclusions: These results demonstrate that shortening the mGFR procedure in individuals with preserved GFR provides similar results to the current standard while significantly decreasing procedure time.