Comparison of 51Cr-EDTA and 99mTc-DTPA for glomerular filtration rate measurement

Purpose The production of Cr-51-labelled ethylenediaminetetraacetic acid (Cr-51-EDTA), a validated and widely used radio-isotopic tracer for glomerular filtration rate (GFR) measurement in Europe, was recently halted by the manufacturer. Technetium-99m-diethylenetriaminepentaacetic acid (Tc-99m-DTPA) clearance has so far mostly been restricted to assessment of separate renal function by scintigraphy, but scarcely used and validated for GFR measurement. We compared the performances of Cr-51-EDTA and Tc-99m-DTPA for GFR and extracellular fluid measurement. Methods In a multi-centre prospective study, Cr-51-EDTA and Tc-99m-DTPA were simultaneously injected into 88 patients, and their urinary and plasma clearances, as well as their volumes of distribution, were measured during seven 30-min periods after a 90-min equilibrium time. Results Mean age was 52.2 +/- 14.5 years, 59% were men. Urinary clearances of Cr-51-EDTA and Tc-99m-DTPA were 64.1 +/- 27.6 and 66.1 +/- 28.0 mL/min, respectively, with a mean bias of 2.00 +/- 2.25 mL/min, an accuracy within 10% of 95% [95% CI 91-99], and a coefficient of determination (R-2) of 0.994. Plasma clearances of Cr-51-EDTA and Tc-99m-DTPA were 66.1 +/- 25.8 and 68.1 +/- 26.6 mL/min, respectively, with a mean bias of 1.96 +/- 3.32 mL/min, an accuracy within 10% of 91% [95% CI 85-97] and a R-2 of 0.985. Distribution volumes were 17.3 +/- 4.6 L for Cr-51-EDTA and 16.6 +/- 4.6 L for Tc-99m-DTPA (R-2 0.930). Conclusion The accuracy and precision of Tc-99m-DTPA clearance, compared to Cr-51-EDTA clearance, was excellent for both urinary and plasma clearance methods, despite an approximate 2 mL/min overestimation, showing that the tracer is a reliable alternative to Cr-51-EDTA for GFR measurement. [GRAPHICS] .