Nuclear medicine scan that assesses renal function, excretion, obstruction.

Indications

• Suspected urinary obstruction
• ...

Phases of renal scan

Study details

• Radiotracers
• DTPA - Measures flow only (GFR). However not useful in low flow states, e.g. renal insufficiency. Otherwise interchangeable with DMSA.
• MAG3 - Measures function and flow. Uptaken into parenchyma and secreted from proximal renal tubules. Better for low flow/GFR as tracer is taken up and then excreted.
• DMSA - binds to proximal renal tubules in renal cortex - shows renal scarring. Can use to differentiate solid renal mass from pseudotumor (normal parenchyma)
• Can have significant radiation burden (almost as much as CT) because the tracer hangs around longer/not excreted; much longer and complicated study compared to MAG3; infants require anesthesia/sedation to keep still
• Polar scarring (e.g. upper/lower) is a/w reflux etiology with UTI
• Clearance
• Patient is asked to void; should visualize sufficient wash-out/clearance of tracer from the kidneys
• If not, may give IV lasix (40 mg in adults) to hasten clearance and re-image in 15-20 minutes
• May want to place Foley catheter if there is concern for reflux producing back-pressure on the system
• Infants will
• Hydro without obstruction - radiotracer is rapidly eliminated ("wash-out")
• Hydro with obstruction - lasix does not produce washout
• Poor renal function/poor hydration - lasix scan becomes less reliable; poor function impairs washout which looks like obstruction
• False positive for obstruction - VUR (reflux and persistent radiotracer)

Function

• In adults, if preserved function > 15%? reasonable to intervene/do reimplant etc
• In children, intervene for function > 10%?