Nuclear medicine · patient guide
MAG3 renogram, dynamic renal scintigraphy for obstruction, split function and renovascular disease.
A MAG3 renogram uses Tc-99m MAG3 to image dynamic kidney function — obstruction (with diuretic), split function and renovascular disease (with captopril). Complements DMSA (cortical) and ultrasound (structural).
Key facts
- 01
Definition
Dynamic Tc-99m MAG3 renal scintigraphy — a nuclear-medicine imaging test of kidney function over time.
- 02
Assesses drainage and split function
Quantifies each kidney’s contribution (split function) and the pattern of drainage from renal pelvis to bladder.
- 03
Diuretic (F-15) protocol
Furosemide is given at 15 minutes to distinguish true obstruction from non-obstructive dilation.
- 04
Captopril protocol
An ACE inhibitor is given to unmask renovascular disease as a cause of hypertension.
- 05
Complements DMSA and ultrasound
DMSA shows cortical scarring; ultrasound shows structure; MAG3 shows dynamic function.
- 06
Consultant-reported
Reported by a consultant in nuclear medicine — the renogram curves are only as useful as the reader.
How the scan is done
From referral to report, what actually happens.
A MAG3 renogram is a specialist test — the sequence below is the same in almost every UK nuclear-medicine department.
- 01
Nephrology or urology referral
A specialist referral defines the clinical question — obstruction, split function, or renovascular disease.
- 02
Hydration before the scan
You are asked to drink plenty of water beforehand — a well-hydrated kidney gives a cleaner curve.
- 03
IV Tc-99m MAG3 injection
A small dose of the radiotracer is injected into a vein in the arm.
- 04
Gamma-camera imaging (30 minutes)
You lie on the couch while a gamma camera images the kidneys continuously for around 30 minutes.
- 05
Furosemide at 15 minutes (F-15)
Where obstruction is the question, IV furosemide is given at 15 minutes to challenge drainage.
- 06
Analysis of renogram curves
The specialist plots uptake and washout curves for each kidney and calculates split function.
- 07
Structured report
A written report — split function percentages, drainage pattern, and a clear conclusion for your referring team.
What it shows
When a MAG3 renogram is the right test.
The scan answers three distinct questions — split function, drainage under diuretic challenge, and renovascular response to captopril.
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Split renal function (%)
The percentage contribution of each kidney to total function — the core MAG3 number.
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Ureteric obstruction
Delayed drainage on the F-15 curve suggests true mechanical obstruction of the ureter.
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Non-obstructive dilation
A dilated system that drains freely after furosemide is baggy, not obstructed.
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Renovascular disease (captopril)
A captopril-provoked drop in function points to renal artery stenosis as a cause of hypertension.
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Post-transplant graft function
Assesses perfusion and drainage of a transplanted kidney.
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Baseline before renal surgery
Establishes function before nephrectomy, pyeloplasty or stone surgery — so change can be measured after.
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Pelvi-ureteric junction obstruction
Confirms or excludes PUJ obstruction in a dilated collecting system.
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Red flag: severe unilateral obstruction with pain — urgent urology
Colicky loin pain with severe obstruction on MAG3 is a same-day urology conversation.
Next steps after the scan
What the report leads to.
A MAG3 renogram is diagnostic — the treatment pathway sits with urology, nephrology or an interventional team. These are the routes it most often points to.
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Observation for non-obstructive dilation
A dilated but well-draining system is often watched with interval imaging rather than operated on.
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Pyeloplasty for PUJ obstruction
Surgical reconstruction of the pelvi-ureteric junction where obstruction is confirmed.
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Ureteric stent
A JJ stent to bridge obstruction — as a temporising measure or ahead of definitive surgery.
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Nephrectomy for a non-functional kidney
Removal considered when split function is very low and the kidney is a source of symptoms.
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Antihypertensive optimisation
For renovascular hypertension — usually the first step, with a repeat scan to gauge response.
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Renal artery stenting (specialist)
Selected renovascular cases are considered for angioplasty and stenting by an interventional team.
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Repeat MAG3 for monitoring
Serial renograms track change in split function and drainage after intervention.
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Structured urology or nephrology follow-up
Every outcome is folded back into a clear specialist plan — not left as a stand-alone report.
Red flags
When a MAG3 result needs an urgent conversation.
These findings — or clinical settings — mean the scan report shouldn’t sit on a desk. Escalate to the relevant specialist team.
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Acute urinary obstruction with pain
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Severe hydronephrosis with sepsis
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Renovascular hypertension
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Post-transplant graft failure
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Ectopic or duplex system with obstruction
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PUJ obstruction with pain
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Suspected malignancy
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Post-op stent migration
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Chronic pyelonephritis with hypertension
Frequently asked
What patients ask about MAG3.
Short answers on how the scan works, how it differs from DMSA, the F-15 and captopril protocols, and radiation dose.
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What is a MAG3 renogram?
A MAG3 renogram is a nuclear-medicine scan that uses a small dose of Tc-99m MAG3 to image how each kidney takes up and drains a tracer over about 30 minutes. It quantifies split function and drainage.
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What is the difference between MAG3 and DMSA?
MAG3 is dynamic — it shows function and drainage over time. DMSA is static and shows cortical scarring. They answer different questions and often complement each other alongside ultrasound.
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What is the F-15 protocol?
F-15 refers to intravenous furosemide given 15 minutes into the scan. It challenges the kidneys to drain and distinguishes true obstruction from a dilated but non-obstructed system.
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What is a captopril MAG3?
A variant where an ACE inhibitor (captopril) is given before the tracer to unmask renovascular disease. A drop in function on the captopril study points to renal artery stenosis.
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How much radiation is involved?
The dose from a MAG3 renogram is small — of the same order as background radiation over a few months. The referring team weighs benefit against dose, especially in younger patients.
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Do I need to prepare?
Good hydration is the main preparation — you will be asked to drink water before the scan. For captopril studies, you may be asked to stop certain blood-pressure medicines beforehand under specialist guidance.
Sources
Guidance we drew on.
Last reviewed 2026-07-30. Next review 2027-07-30. Reviewed by Pulse Atlas Editorial Board ().
- British Nuclear Medicine Society. Guidance on renal radionuclide imaging.
- European Association of Nuclear Medicine. Procedure guideline for MAG3 renography.
- Renal Association (UK Kidney Association). Clinical practice guidelines.
- British Association of Urological Surgeons. Guidance on upper-tract obstruction.
Related tests
Looking for a different test?
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DMSA scan
Static cortical scintigraphy — the scarring test that complements MAG3.
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Ultrasound
Structural imaging of the kidneys and collecting system — usually the first step.
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In practice, in London
What mag3 renogram looks like on the ground in London
With mag3 renogram, the London question is usually about report turnaround and the radiologist reading it — not whether the scan is available. The NHS route for mag3 renogram is thorough, but the queue is real. Most patients we speak with have been told to expect anywhere from a handful of weeks to several months, depending on their local trust and how the referral is graded. Going private in London usually collapses that window to a matter of days — often the same week if the diary allows. It isn’t about jumping a queue so much as buying time back while you still have the flexibility to plan around it.
Once you’re in the private system for mag3 renogram, the pace picks up noticeably. Consultant slots run to time, imaging is usually available in the same building or a short walk away, and the report comes back typed and detailed. It’s the coordination that tends to feel different — one person on the other end of the phone, not a switchboard. For mag3 renogram specifically, the difference between a routine report and a sub-speciality read is where private care earns its keep.
There are a lot of consultants in London who can technically handle mag3 renogram. Fewer who do it week in, week out for the exact question you’re bringing. We spend most of our time working out which is which — and being straight when a different test or a different specialist would serve you better. Everything runs to CQC, GMC and Royal College standards; the choice is about fit, not floor.