Accurate and precise plasma clearance measurement using four 99mTc-DTPA plasma samples over 4 h

Area of Science:

• Nephrology
• Nuclear Medicine
• Pharmacokinetics

Background:

• Glomerular filtration rate (GFR) is crucial for assessing kidney function.
• Current GFR measurement methods often require numerous, prolonged blood samples, which can be challenging for patients, especially children.
• There is a need for simplified, accurate, and precise GFR measurement techniques.

Purpose of the Study:

• To evaluate and compare two plasma concentration curve area methods for calculating GFR clearance (CL).
• To determine if reduced sampling times (4 hours with 4 samples) can maintain accuracy and precision compared to standard methods (8 hours with 9 samples).

Main Methods:

• Comparison of GFR clearance (CL) values derived from biexponential fitting [CL (E2)] and Tikhonov adaptively regularized gamma variate fitting [CL (Tk-GV)].
• Analysis of 412 Tc-DTPA studies in 142 patients, primarily pediatric, with suspected fluid disturbances.
• Evaluation of 4 versus 8-hour time samplings (4 samples vs. 9 samples).

Main Results:

• CL (Tk-GV) using 4 samples/4h and 9 samples/8h showed accurate and precise agreement with the standard method (noncompartmental numerical integration [CL (NI)]).
• The biexponential fitting method [CL (E2)] significantly overestimated CL (NI) values by 4.9% (4 samples/4h) and 3.8% (9 samples/8h).
• CL (Tk-GV) demonstrated accuracy and precision comparable to the standard method with reduced sampling.

Conclusions:

• The biexponential fitting method [CL (E2)] is inaccurate and imprecise for GFR clearance calculation and should be replaced.
• The Tikhonov adaptively regularized gamma variate fitting [CL (Tk-GV)] method allows for a significant reduction in sampling time (from 8 to 4 hours) and sample number (from 9 to 4).
• CL (Tk-GV) offers a precise, accurate, simplified, and more tolerable method for GFR testing.