MAG3 Diuretic Renogram

The diuretic (furosemide) renogram uses Tc-99m MAG3, a tubular agent with high extraction efficiency, to assess split renal function and to distinguish true obstruction from a baggy, non-obstructed dilated collecting system. Dynamic imaging generates time-activity (renogram) curves for each kidney; a diuretic challenge tests whether a dilated system washes out promptly (non-obstructed) or retains tracer (obstructed). It is the standard functional test for equivocal hydronephrosis and for quantifying differential function before intervention.

Indications

Differentiation of obstructive from non-obstructive hydronephrosis / pelvicalyceal dilatation
Quantification of split (differential) renal function before nephrectomy or pyeloplasty
Assessment of pelviureteric or vesicoureteric junction obstruction, including in children
Evaluation of renal transplant perfusion, function and possible obstruction or leak
Screening for renovascular hypertension using captopril/ACE-inhibitor renography

Contraindications & Cautions

Pregnancy is a relative contraindication; justify and minimise dose
Breastfeeding: interruption is generally not required for Tc-99m MAG3 but local guidance may advise brief precautions for free pertechnetate
Furosemide allergy or significant hypovolaemia/hypotension — correct before diuretic administration
For captopril studies, withhold if the patient is volume-depleted or has critical bilateral renal artery/solitary-kidney stenosis (risk of acute kidney injury)
Dehydration invalidates the diuretic response — ensure adequate hydration before the study

Patient Preparation

Ensure good hydration (oral or IV ~10 mL/kg) so the diuretic response is valid
Encourage the patient to void immediately before imaging; consider bladder catheterisation in infants or with a full/neurogenic bladder
For renovascular studies, withhold ACE inhibitors/ARBs per protocol before captopril administration
Explain the need to lie still supine over the camera for 20-30 minutes
Confirm pregnancy status and recent contrast or diuretic use

Technique & Parameters

Inject Tc-99m MAG3 (typically 40-370 MBq; lower weight-based dose in children) as a bolus with the patient supine, camera posterior
Acquire a dynamic sequence for ~20-30 minutes with the kidneys and bladder in the field of view
Administer furosemide 0.5 mg/kg IV using an F+20 (20 min after tracer), F0 (with tracer) or F−15 (15 min before tracer) protocol
Generate whole-kidney and cortical regions of interest with background subtraction to derive renogram curves
Calculate split function from the uptake (2-3 min) phase and washout half-time (t1/2) after diuretic

Systematic Review

Assess symmetry of tracer arrival, cortical uptake and transit for each kidney
Compute split (differential) function, normally close to 50:50 (each kidney ~45-55%)
Classify the renogram curve shape (normal rising-then-falling, plateau/accumulating, or obstructive)
Evaluate the response to furosemide — prompt washout versus continued accumulation
Check the bladder and any collecting-system stasis, and correlate with anatomy

Key Findings & Significance

Diuretic washout half-time <10 minutes indicates a non-obstructed system
Washout half-time >20 minutes indicates obstruction; 10-20 minutes is equivocal/indeterminate
A prompt fall in the curve after furosemide in a dilated system indicates dilatation without obstruction
Persistently rising ("accumulating") curve unresponsive to diuretic supports true obstruction
Split function <40-45% in the affected kidney quantifies functional impairment and guides intervention

Differential Considerations

Retained tracer in a dilated pelvis: true obstruction versus reservoir effect of a capacious non-obstructed system
Poor diuretic response: obstruction, dehydration, poor baseline renal function, full bladder
Reduced split function: chronic obstruction, reflux nephropathy, renal artery stenosis, dysplasia
Delayed cortical transit on captopril study: renovascular hypertension (haemodynamically significant stenosis)
Photopenic transplant with poor perfusion: acute tubular necrosis, rejection, vascular compromise or urine leak

Pearls & Pitfalls

A poor diuretic response can be false in dehydration, a full bladder or poor renal function — ensure hydration, drainage and adequate baseline uptake
Gravity-assisted (post-void, upright/delayed) imaging can resolve equivocal washout in a baggy system
MAG3 is preferred over DTPA in impaired renal function and neonates because of higher extraction efficiency
Split function is derived from the uptake phase (1-2.5 min), before excretion, and is the key surgical parameter
For renovascular hypertension, a curve that worsens after captopril compared with baseline supports a functionally significant stenosis

Structured Report

State tracer, activity, hydration, diuretic protocol (F+20/F0/F−15) and bladder management
Report split function for each kidney and the renogram curve pattern
Give the diuretic washout half-time with the interpretive thresholds
Conclude on the presence or absence of obstruction and the functional significance
Recommend follow-up or intervention where relevant and correlate with anatomical imaging

References

SNMMI Procedure Standard / EANM Practice Guideline for Diuretic Renography 4.0
Taylor AT, et al. SNMMI/EANM procedure standard for diuretic renography in adults. J Nucl Med 2018
Gordon I, et al. Guidelines for standard and diuretic renogram in children (EANM)
Blaufox MD, et al. Report of the radionuclides in nephrourology consensus. J Nucl Med

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.

MAG3 Diuretic Renogram

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References