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Renal scintigraphy — MAG3, DTPA and DMSA

Each renal tracer measures a different function: DTPA is filtered by the glomerulus and measures GFR, MAG3 is secreted by the tubules and suits a weak kidney and obstruction, and DMSA binds the cortex and shows scars and split function.

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Why it matters in the exam

The exam asks when to choose each tracer and how to interpret a diuretic renogram. MAG3 is cleared from blood far more efficiently than DTPA, so the image is better in a weak kidney, in neonates and in obstruction; DTPA is the tracer for calculating GFR. In a dynamic renogram the time-activity curve is examined: uptake phase, peak and drainage phase. When the renal pelvis is dilated furosemide is given: rapid drainage after the diuretic (half-time under 10 minutes) excludes obstruction, slow drainage (over 20 minutes) fits obstruction, and between 10 and 20 minutes is equivocal.

Causes of "false" obstruction: poor renal function that does not respond to the diuretic, a very dilated pelvis (large reservoir), a full bladder, dehydration and lying flat only. So hydration, voiding or a catheter, and an image after standing are requested. Normal split function is about 45%–55% for each kidney. Captopril (ACE inhibitor) renography was used to investigate renovascular hypertension — a fall in function on the affected side after the drug — and today has largely been replaced by anatomical imaging.

DMSA is taken up by the proximal tubules and imaged about 2–4 hours after injection; in acute pyelonephritis "cold" areas are seen, and a scar is defined only on a scan at least 6 months after the infection. DMSA is also used for an ectopic kidney and split function. In renal transplantation: acute tubular necrosis (ATN) — preserved perfusion with poor excretion; acute rejection — falls in both perfusion and function; urine leak — tracer outside the urinary tract. The Hilson index compares iliac artery flow with flow in the graft, and a higher value indicates poorer perfusion. Radionuclide cystography diagnoses vesicoureteric reflux with less radiation than VCUG and suits follow-up.

Key points

• DTPA — GFR; MAG3 — tubular secretion; DMSA — cortex.
• Drainage half-time under 10 minutes excludes obstruction; over 20 — obstruction.
• Normal split function 45%–55%.
• Scar on DMSA — at least 6 months after infection.
• Graft: ATN — perfusion preserved; rejection — both reduced.

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Sources

• SNMMI Procedure Standard for Diuretic Renography in Adults with Suspected Upper Urinary Tract Obstruction, 2018 — Tracers, diuretic timing and interpretation
• EANM Guidelines on Renal Cortical Scintigraphy in Children, 2017 — DMSA indications and timing
• SNMMI/EANM Practice Guideline for Renal Transplant Scintigraphy, 2018 — Perfusion and function patterns

Sources are given for further reading; the text is written afresh and not copied from them.

Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.