GFR Measurement⁹⁹ᵐTc-DTPA (or ⁵¹Cr-EDTA)
Camera-based (Gates) and plasma-clearance methods for glomerular filtration rate
Quick Answer
Radionuclide GFR provides a measured (not estimated) glomerular filtration rate using a purely filtered tracer — Tc-99m-DTPA or Cr-51-EDTA. Two approaches: the camera-based Gates method derives GFR from the fraction of injected activity taken up by the kidneys over the first few minutes (with depth/attenuation correction), while plasma-sampling clearance measures the tracer's disappearance from blood over time. Measured GFR is used where accuracy matters — chemotherapy dosing, potential kidney donors, and discordant eGFR.
Methods
- Gates (camera) method: GFR from renal uptake as a percentage of injected dose, corrected for renal depth (from height/weight) and background; also yields split GFR by combining with differential function.
- Plasma clearance: single- or multiple-sample blood measurements after a filtered-tracer bolus; considered the more accurate radionuclide method.
When measured GFR is preferred
- Cytotoxic/chemotherapy dosing (e.g. carboplatin) requiring an accurate absolute GFR.
- Potential living kidney donors (absolute and split function).
- Discrepant or unreliable creatinine-based eGFR (extremes of body habitus, amputees, unstable function).
Measured, not estimated — and split matters
Radionuclide GFR gives a measured (not creatinine-estimated) filtration rate using a purely filtered tracer (Tc-99m-DTPA or Cr-51-EDTA, not the tubular agent MAG3). Plasma-sampling clearance is the more accurate method; the camera-based Gates method is faster and additionally yields split GFR (= total measured GFR × differential function) — the actionable number before nephrectomy or living kidney donation. Reach for measured GFR when accuracy matters: carboplatin/chemo dosing, donor evaluation, or discordant eGFR.
High-Yield Pearls
- Split GFR = measured total GFR × differential function — the actionable number before nephrectomy/donation.
- Plasma-sampling clearance is generally more accurate than camera Gates; Gates is faster and gives split function.
- Uses a filtered tracer (DTPA/EDTA), not the tubular agent MAG3.
Common Pitfalls
- Depth/attenuation-correction errors in the Gates method (body habitus).
- Extravasated injection invalidating the injected-dose reference.
Related Pages
- Tracer: Tc-99m-DTPA / Cr-51-EDTA (filtered); contrast: MAG3 (tubular, for renography).
Self-Check
Q1. Why must GFR use a filtered tracer (DTPA/EDTA) rather than MAG3?
Answer: GFR requires a purely glomerular-filtered tracer; MAG3 is tubularly secreted, so it measures effective renal plasma flow, not filtration.
Q2. Which radionuclide GFR method is generally more accurate, and which additionally yields split GFR?
Answer: Plasma-sampling clearance is more accurate; the camera-based Gates method is faster and gives split GFR.
Q3. Give two clinical situations where measured (not estimated) GFR is preferred.
Answer: Carboplatin/chemotherapy dosing and living kidney-donor evaluation (also discordant/unreliable creatinine-based eGFR).
Q4. How is split GFR calculated and why does it matter before nephrectomy?
Answer: Split GFR = total measured GFR × differential function — the actionable per-kidney number before nephrectomy or donation.
Evidence & sources
https://nuc.med/gfr-measurement/ Report an issue