99mTc DTPA vs. 51Cr EDTA for glomerular filtration rate measurement: is there a systematic difference?

Aim The study aimed to investigate whether a systematic difference exists between Cr-51 EDTA and Tc-99m DTPA for measurement of glomerular filtration rate (GFR). Methods The distribution of GFR results from candidates attending the Royal Free Hospital for assessment of suitability for kidney donation was compared before and after the change from Cr-51 EDTA to Tc-99m DTPA using three-sample slope-intercept GFR calculation with samples at 2, 3, and 4 hours. A second cohort of oncology patients attending Leeds Teaching Hospitals NHS Trust underwent simultaneous GFR measurement with both tracers by full characterisation of the plasma clearance curve with nine samples between 5 minutes and 8 hours post-injection. Three-sample slope-intercept GFR was also calculated for comparison with cohort 1. Results From the first cohort, a statistically significant (P= 0.008) systematic difference of 5.8% (95% confidence interval: 1.5%-10.1%) was found in the three-sample slope-intercept GFR, with Tc-99m DTPA giving the higher result. From the second cohort, a statistically significant (P= 0.00001) systematic difference of 2.9% (95% confidence interval: 1.8%-3.9%) was found in three-sample slope-intercept GFR, with Tc-99m DTPA giving the higher result. There was no statistically significant difference between the tracers when GFR was calculated by full characterisation of the plasma clearance curve. Conclusion There is a small systematic difference between GFR measured with Tc-99m DTPA and Cr-51 EDTA using abbreviated techniques, which is removed when GFR is calculated by full characterisation of the plasma clearance curve. The difference is not clinically significant in the context of intra-patient variability of GFR measurement. Copyright (C) 2019 Wolters Kluwer Health. Inc. All rights reserved.