51Cr-EDTA plasma clearance in children: One, two, or multiple samples?

Area of Science:

• Nephrology
• Pharmacokinetics
• Biomedical Engineering

Background:

• Plasma disappearance curves with multiple blood samples are a reference for measuring glomerular filtration rate (GFR).
• No established protocol exists for this GFR measurement technique.
• Two-compartment models are typically used for concentration-time decay curves, but fitting procedure impacts are unexamined.

Purpose of the Study:

• To evaluate the impact of different fitting procedures on GFR calculations from plasma disappearance curves.
• To compare GFR results from various fitting methods with late-sample and one-sample methods.
• To assess the robustness and reliability of different GFR measurement protocols.

Main Methods:

• Defined 8 distinct fitting procedures to calculate area under the curve and subsequent GFR.
• Applied these 8 methods to multiple blood sample data (8 samples) from 20 children with Duchenne muscular dystrophy.
• Compared results with GFR values derived from late samples (post-120 minutes) and one-sample methods.

Main Results:

• In 6 of 20 cases, full curve fitting procedures yielded highly variable GFR values (0-120 mL/min) or failed to fit data.
• Reported GFR is highly dependent on the fitting method, indicating reduced robustness of the full curve approach.
• Late-sample and one-sample methods demonstrated robustness, with no fitting issues and acceptable accuracy compared to a consensus GFR.

Conclusions:

• The choice of fitting method significantly impacts GFR results, challenging the robustness of full concentration-time curve analysis.
• Late-sample methods (using 3 time-points) are robust and reliable for determining GFR.
• One-sample methods also provide acceptable accuracy for GFR assessment.