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Published on: May 10, 2013
99mTc DTPA vs. 51Cr EDTA for glomerular filtration rate measurement: is there a systematic difference?
Helena McMeekin1, Mark Barnfield2, Fred Wickham3
1Department of Nuclear Medicine, Barts Health NHS Trust, London.
Insights
A small systematic difference in glomerular filtration rate (GFR) measurements exists between chromium ethylenediaminetetraacetic acid (Cr EDTA) and technetium diethylenetriaminepentaacetic acid (Tc DTPA) when using abbreviated calculation methods. This difference is negligible when GFR is determined by full plasma clearance curve characterization.
Area of Science:
- Nephrology
- Radiopharmacology
- Medical Imaging
Background:
- Glomerular filtration rate (GFR) is a key indicator of kidney function.
- Chromium ethylenediaminetetraacetic acid (Cr EDTA) and technetium diethylenetriaminepentaacetic acid (Tc DTPA) are commonly used radiotracers for GFR measurement.
- Abbreviated GFR calculation methods are widely employed for efficiency.
Purpose of the Study:
- To determine if a systematic difference exists between Cr EDTA and Tc DTPA in GFR measurements.
- To compare GFR results obtained using abbreviated techniques versus full plasma clearance characterization.
Main Methods:
- Comparison of GFR results from two patient cohorts before and after a change in tracer from Cr EDTA to Tc DTPA.
- Utilized three-sample slope-intercept GFR calculation (2, 3, and 4-hour samples) in the first cohort.
- Performed simultaneous GFR measurements with both tracers using full plasma clearance curve characterization (nine samples, 5 minutes to 8 hours) in the second cohort.
Main Results:
- A statistically significant systematic difference of 5.8% was observed in the first cohort using the three-sample method, with Tc DTPA yielding higher GFR values (P = 0.008).
- A statistically significant systematic difference of 2.9% was found in the second cohort using the three-sample method, with Tc DTPA yielding higher GFR values (P = 0.00001).
- No statistically significant difference was detected between the tracers when GFR was calculated by full plasma clearance curve characterization.
Conclusions:
- Abbreviated GFR measurement techniques using Tc DTPA and Cr EDTA exhibit a small systematic difference.
- This systematic difference is eliminated when employing full plasma clearance curve characterization for GFR calculation.
- The observed difference is not clinically significant when considering the intra-patient variability of GFR measurements.
Aim:
The study aimed to investigate whether a systematic difference exists between Cr EDTA and Tc 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 EDTA to Tc 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 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 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 DTPA and Cr 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.
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