Optimizing Glomerular Filtration Rate Estimation: A Simplified Method for Improved Accuracy and Efficiency

The glomerular filtration rate (GFR) is a key measure of renal function, typically estimated using creatinine-based equations. More precise clearance measurements are obtained with radiotracers, such as [^99mTc]Tc-diethylenetriaminepentaacetic acid (DTPA), and blood samples over several hours. However, standard plasma clearance methods require labor-intensive plasma preparation, limiting efficiency in clinical practice. This study proposes a simplified approach to GFR estimation by directly measuring radioactivity in whole blood and applying a correction factor based on hematocrit, eliminating the need for blood centrifugation and reducing calibration steps. Methods: Sixty-seven adults and children undergoing GFR assessment with [^99mTc]Tc-DTPA were included in the study. GFR was estimated using both the standard plasma-based method and a whole-blood approach, which directly measured radioactivity in whole blood and applied a correction factor based on hematocrit. The γ-counter's response linearity and reproducibility were assessed to validate the correction factor. Comparisons between plasma-based and whole blood-derived GFRs were performed using linear regression and deviation analysis. Results: The γ-counter demonstrated a detection efficiency of 50.5% in the activity range of 30-150 kBq, confirming its reliability for whole-blood measurements. The proposed whole-blood method yielded GFRs that were highly correlated with the plasma-based approach, with an average deviation of 4%. Significant deviations (>15%) were observed in only 2 of 67 cases. The whole-blood method eliminated the need for plasma separation, reduced processing time, and maintained measurement accuracy. Conclusion: The proposed whole-blood approach provides a reliable alternative to standard plasma-based GFR estimation, simplifying sample preparation and reducing clinical workload. This method enhances efficiency in nuclear medicine while preserving measurement accuracy, making it a viable option for routine renal function assessment.