European Nuclear Medicine Guide
[99mTc]Tc-diethylenetriaminepentaacetic acid, also known as
[99mTc]Tc-DTPA is a radiopharmaceutical used mainly for renal dynamic imaging. Its renal extraction is around 20% [126]. Following intravenous administration, it is entirely filtered by glomeruli in the kidneys. A lower rate of glomerular filtration compared with inulin is probably due to protein binding, the amount of which varies, with the formulation, between 5 and 10% in 1 h. A maximum concentration of 5% in each kidney is achieved 2-3 min after injection. Urinary excretion amounts to about 90% in 24 h [132,133].
Although [51Cr]Cr-EDTA is probably the best tracer for measurement of GFR, [99mTc]Tc-DTPA is a valid alternative, especially when [51Cr]Cr-EDTA is not commercially available and/or a well counter is not accessible locally. It has the following advantages over [51Cr]Cr-EDTA: it is less expensive, has a higher counting efficiency, and measurement of injected activity can be assessed with sufficient precision on an isotope calibrator.
The use of [99mTc]Tc-DTPA for the calculation of GFR was validated 25 years ago and more recently, its protein binding was demonstrated to be not significantly different than the one of [51Cr]Cr-EDTA [127,134].
The suggested activity to administer is scaled on a body surface basis with a maximum of 37 MBq (children)
The effective dose for [99mTc]Tc-DTPA is 4.9 µSv/MBq for patients with normal renal function and 4.6 µSv/MBq with abnormal renal function [3]. The organ with the highest absorbed dose is the urinary bladder wall: 62 µGy/MBq
The effective dose for [99mTc]Tc-DTPA is: 0.98 mSv per procedure.
Caveat:
“Effective Dose” is a protection quantity that provides a dose value related to the probability of health detriment to an adult reference person due to stochastic effects from exposure to low doses of ionizing radiation. It should not be used to quantify the radiation risk for a single individual associated with a particular nuclear medicine examination. It is used to characterize a certain examination in comparison to alternatives, but it should be emphasized that if the actual risk to a certain patient population is to be assessed, it is mandatory to apply risk factors (per mSv) that are appropriate for the gender, the age distribution and the disease state of that population."
In terms of clinical report, the following data should be included:
The clearance of [99mTc]Tc-DTPA is recognized has being systematically higher than the one of [51Cr]Cr-EDTA [134,135]. As such, for serial measurements on the same patient the same radiopharmaceutical should be used, and preferably the same manufacturer.
If [99mTc]Tc-DTPA is used for both the measurement of GFR and for renography, both tests can be performed on the same day provided that furosemide is not administered for the scintigraphic study, since there is a possibility that the diuretic influences the value of the GFR.
The main precautions to be observed are similar to the ones referred for the measurement of GFR with [51Cr]Cr-EDTA.
The considerations are the same as those referred for the measurement of GFR with [51Cr]Cr-EDTA, namely hydration, ingestion of food and drinks, and restriction to physical activity.
It is not necessary to interrupt breast feeding after administration of [99mTc]Tc-DTPA (2). Nevertheless, previous to initiating the examination, the presence of pregnancy and breast-feeding should be questioned, and the benefit-risk balance should be evaluated.
The “slope-intercept method using 2 to 4 blood samples or the single-sample method can be used to measure GFR with [99mTc]Tc-DTPA [114,131,134].
Detailed recommendations regarding the paediatric procedures are available in the EANM Paediatrics Guidelines [113].