Renal Scan (Tc-99m MAG3 +/- Lasix)

Indications

• Obstructive vs nonobstructive hydronephrosis (diuretic renography)
• Differential (split) renal function
• Renovascular hypertension (with ACE inhibitor)
• Renal transplant evaluation (perfusion, function, urine leak/obstruction)
• Assessment of post-surgical drainage

Patient prep

• Hydrate orally (well-hydrated essential for diuretic study)
• Empty bladder before exam; bladder catheter if needed (transplant, neonate, poor voiding)
• Hold ACE inhibitors for captopril renography per protocol
• No fasting required

Contrast

Technique

• LEHR collimator, 140 keV, posterior detector (anterior for transplant in pelvis)
• Dynamic acquisition: flow phase 1-3 sec/frame x 60 sec, then 15-30 sec/frame for 20-30 min
• Furosemide (Lasix) 0.5 mg/kg IV (typically 20-40 mg adult) for diuretic challenge
• Generate renogram curves; calculate split function and T1/2 washout

Series / Sequences

Key points

• Diuretic washout T1/2 <10 min = nonobstructed; >20 min = obstructed; 10-20 min = equivocal
• Adequate hydration and an empty bladder are essential for valid diuretic interpretation
• Full bladder or dehydration causes false-positive obstruction pattern
• MAG3 preferred over DTPA in impaired renal function (higher extraction)
• Captopril/ACE-inhibitor study for renovascular HTN compares baseline vs post-ACEi

References