Tc-99m-DTPA⁹⁹ᵐTc-DTPA
A glomerular-filtration agent for GFR, dynamic renography, and aerosol ventilation
Quick Answer
Tc-99m-DTPA is cleared by glomerular filtration, making it the agent for GFR measurement (camera-based Gates method or plasma clearance) and an alternative for dynamic renography. Its lower extraction than MAG3 gives poorer images in impaired renal function, so MAG3 is preferred when function is reduced. As a nebulized aerosol it also serves as a V/Q ventilation agent, and its bolus is used for radionuclide angiography/flow studies.
Mechanism
DTPA is freely filtered at the glomerulus and neither secreted nor reabsorbed — a true filtration marker (hence GFR). Its single-pass extraction is lower than MAG3's (which is actively secreted), so DTPA gives higher background and poorer images when renal function is impaired.
Biodistribution
Kidneys/collecting system and bladder; higher soft-tissue background than MAG3. As an aerosol, deposition in the airways/alveoli (central "hot spots" in obstruction).
Clinical Indications
- GFR quantification: Gates camera method or plasma-sampling clearance.
- Dynamic renography where MAG3 is unavailable (less ideal in renal impairment).
- Aerosol ventilation for V/Q (central deposition in airflow obstruction).
- Radionuclide angiography / flow (transplant perfusion, brain-death flow — crosses a disrupted blood–brain barrier).
MAG3 vs DTPA (Quick Contrast)
| MAG3 | DTPA | |
|---|---|---|
| Handling | Tubular secretion (high extraction) | Glomerular filtration |
| Best for | Dynamic function/drainage, poor renal function | GFR measurement |
| Image quality in CKD | Better | Worse (low extraction) |
Reporting Checklist
- GFR: report the method (Gates vs plasma clearance) and split GFR where relevant.
- Renography: curve/drainage as per the renal-scintigraphy protocol (prefer MAG3 in poor function).
- Ventilation: note central "hot-spot" deposition in obstruction.
Common Pitfalls
- Using DTPA in significant renal impairment (poor target-to-background) instead of MAG3.
- Aerosol clumping artifacts in COPD (central hot spots).
- Extravasated injection invalidating GFR's injected-dose reference (Gates).
Board Pearls
DTPA is cleared by glomerular filtration — not secreted or reabsorbed — making it a true GFR marker (Gates camera method or plasma clearance). Its lower single-pass extraction than MAG3 means poorer images in impaired function, so MAG3 is preferred when renal function is reduced.
As a nebulized aerosol, DTPA is a V/Q ventilation agent (central "hot spots" in airflow obstruction); as a bolus it serves radionuclide angiography/flow (transplant perfusion, brain-death flow).
The unifying theme is a small, freely-filtered, non-reabsorbed molecule. It crosses a disrupted blood–brain barrier (historical brain-flow use), and its filtration handling is exactly why it measures GFR while MAG3 (tubular) better reflects effective renal plasma flow and images better in CKD.
Related Pages
- Tracer/protocol: MAG3, renal scintigraphy, GFR measurement; ventilation: ventilation agents, V/Q scan & PE.
- Pitfalls: Pearls, pitfalls & normal variants.
Figure / Diagram Suggestions
- A filtration-vs-secretion nephron schematic (DTPA vs MAG3).
- A Gates-method GFR calculation diagram.
- An aerosol central-deposition COPD teaching image.
Self-Check (Board-Style)
Q1. Why is MAG3 preferred over DTPA for dynamic renography in a patient with poor renal function?
Answer: MAG3's high tubular extraction gives much better target-to-background images than filtered DTPA when function is reduced.
Q2. What makes DTPA a valid GFR marker?
Answer: It is freely filtered at the glomerulus and neither secreted nor reabsorbed — a true filtration marker.
Q3. Aerosol DTPA shows central "hot spots." In what condition, and why?
Answer: Airflow obstruction (COPD) — turbulent flow causes central airway deposition/clumping of the aerosol.
Q4. Besides renal and ventilation studies, name a flow application of Tc-99m-DTPA.
Answer: Radionuclide angiography/flow — e.g. transplant perfusion or brain-death flow studies (it crosses a disrupted blood–brain barrier).
Evidence & sources
https://nuc.med/tc99m-dtpa/ Report an issue