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IMAGE INTERPRETATION · RENAL AND GENITOURINARY

Furosemide Dose for Diuretic Renography

Tc-99m MAG3 qualitative renal scan with quantitative parameters: Right T½ = 22.2 min, residual 30 min = 49.4%; Left T½ = 8.1 min, residual 30 min = 15.9%; equal bilateral differential function (51%/49%)
Tc-99m MAG3 qualitative renal scan with quantitative parameters: Right T½ = 22.2 min, residual 30 min = 49.4%; Left T½ = 8.1 min, residual 30 min = 15.9%; equal bilateral differential function (51%/49%)

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Question

During a diuretic renal scan (MAG3 with Lasix), furosemide is injected to help determine whether retained tracer in the collecting system is due to true obstruction or just a dilated but non-obstructed system. As the nuclear medicine technologist performing this study, what is the STANDARD adult dose and route of administration for furosemide?

  1. A20 mg administered orally 1 hour before the scan begins, to ensure adequate diuresis during the imaging period
  2. B40 mg (0.5 mg/kg) administered intravenously during the scan, typically at 20 minutes post-injection or when the collecting system is well-visualized
  3. C100 mg administered intramuscularly at the start of the scan, allowing gradual absorption to produce sustained diuresis throughout imaging
  4. D10 mg administered as a subcutaneous injection 30 minutes before the radiopharmaceutical, to pre-hydrate the collecting system prior to tracer arrival
Show the answer and explanation

B. 40 mg (0.5 mg/kg) administered intravenously during the scan, typically at 20 minutes post-injection or when the collecting system is well-visualized

The standard furosemide (Lasix) dose for a diuretic renogram is 0.5 mg/kg IV (maximum 40 mg for adults). It is administered intravenously — either at the start of the study (F+0 protocol), 15–20 minutes into the scan (F+20 protocol, most common), or 15 minutes before the radiopharmaceutical (F-15 protocol). The IV route ensures rapid onset of diuresis. The resulting increased urine flow will wash out tracer from a non-obstructed dilated system (T½ <10 min post-Lasix) but will fail to clear a truly obstructed system (T½ >20 min post-Lasix).

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