Optimization of Time Interval for Plasma Counting in Plasma Sampling Method for GFR Estimation

Objectives: Glomerular filtration rate (GFR) is an important diagnostic measure of kidney function. The plasma sampling method is considered a gold standard for GFR estimation, but it is time-consuming for postgate GFR scans and requires expertise. The aim of this study is to identify the optimal time point to perform counting for GFR using the plasma sampling method without significant deviation from the established results. Material and Methods: Twenty-five patients (15 males and 10 females; average age 47 years) who underwent GFR evaluation by the double-plasma sampling method were included. Two plasma samples were collected at 2 and 4 h postadministration of 99mTc-diethylenetriaminepentaacetic acid. Counts were obtained at 4 h, 12 h, and 24 h postsampling. GFR was calculated using an in-house software developed for GFR estimation. Data were statistically analyzed for correlation using Microsoft Excel 2013. Results: The average GFR estimates were 47.99 ± 31.32, 58.42 ± 32.96, and 59.88 ± 32.99 mL/min at 4 h, 12 h, and 24 h, respectively. The mean GFR estimated by the Gates’ method was 57.86 ± 32.15 mL/min. The correlation coefficient between the 12-h and 24-h counts was 0.98, significantly better than the 4-h count (−0.32). The percentage difference in GFR estimates between the Gates method and the plasma sampling method was 21% at 4 h, while the differences at 12 h and 24 h ranged from 1% to 3%. Conclusion: Our study suggests that a 12-h interval is the optimal time for counting the plasma samples for GFR calculation. This provides results comparable to 24-h counts but with a significantly faster reporting time. Reducing delays in diagnosis and treatment can improve patient management.