Comparison of Tc-DTPA and Cr-EDTA for Glomerular Filtration Rate Measurement with the Continuous Infusion Method

Background: In late 2018, the production of Chromium-labelled ethylenediamine tetra-acetic acid (Cr-EDTA), a validated and widely used radio-isotopic tracer for measuring glomerular filtration rate, was halted. Technetium-99m-diethylenetriaminepentaacetic acid (Tc-DTPA) has been validated for GFR measurement with a single bolus injection, a procedure not suitable in patients with extracellular compartment hyperhydration. In such cases, a bolus followed by continuous infusion of the tracer is required. The aim of this study was to evaluate whether Tc-DTPA with the infusion protocol can replace Cr-EDTA for GFR measurement.

Methods: We conducted a prospective single centre study during February and March 2019. All patients referred for GFR measurement received both radiotracers simultaneously: Cr-EDTA and Tc-DTPA bolus and continuous infusion were administered concomitantly through the same intravenous route. Over four and a half hours, plasma and urine samples were collected to calculate urinary and plasma clearance.

Results: Twenty-two patients were included (mean age 63.4 ± 17.5 years; 68% men). Mean urinary clearance of Cr-EDTA and Tc-DTPA was 52.4 ± 22.5 mL/min and 52.8 ± 22.6 mL/min, respectively (p = 0.47), with a mean bias of 0.39 ± 2.50 mL/min, an accuracy within 10% of 100% (95% CI 100; 100) and a Pearson correlation coefficient of 0.994. Mean plasma clearance of Cr-EDTA and Tc-DTPA was 54.8 ± 20.9 mL/min and 54.4 ± 20.9 mL/min, respectively (p = 0.61), with a mean bias of - 0.43 ± 3.89 mL/min, an accuracy within 10% of 77% (95% CI 59; 91) and a Pearson correlation coefficient of 0.983.

Conclusions: Urinary and plasma clearance of Tc-DTPA can be used with the infusion protocol to measure GFR.