Causes of False Negative Diuretic Renogram in Upper Urinary Tract Obstruction
False negative diuretic renograms in upper urinary tract obstruction are most commonly caused by dehydration, early obstruction, severe renal impairment, and compression of the renal pelvis or ureters by tumor or fibrosis. 1
Primary Causes of False Negative Results
Dehydration: Inadequate hydration status can mask obstruction by reducing urine production and flow, preventing the characteristic obstructive pattern from developing during the study 1
Early or acute obstruction: Recently developed obstruction may not yet demonstrate the classic findings of obstruction on diuretic renography 1
Severe renal impairment: Kidneys with significantly reduced function may not produce enough urine to generate an obstructive pattern even when obstruction exists 2
Extrinsic compression: Compression of the renal pelvis or ureters by tumor or retroperitoneal fibrosis can cause functional obstruction while allowing some drainage, leading to false negative results 1
Suboptimal image quality: Technical factors affecting image acquisition can lead to misinterpretation of results 1
Anatomical and Functional Factors
Duplex collecting systems: Obstruction in one segment of a duplex kidney, particularly if poorly functioning, may be missed on standard diuretic renography 2
Megaureters with reflux: Severe reflux with megaureters can mask obstruction by allowing retrograde filling and apparent drainage 2
Intermittent obstruction: Obstruction that is positional or intermittent may not be present during the study period 1
Technical and Protocol-Related Factors
Timing of diuretic administration: The standard F+20 protocol (furosemide given 20 minutes after radiotracer) has a higher rate of equivocal or false negative results compared to F+0 (simultaneous administration) or F-15 (furosemide given 15 minutes before radiotracer) protocols 3, 4
Inadequate diuretic effect: Poor response to the diuretic can prevent the provocation of obstruction 5
Choice of radiotracer: DTPA (diethylenetriamine pentaacetic acid) is less efficiently extracted by the kidney compared to tubular tracers like MAG3 (mercaptoacetyltriglycine), potentially leading to false negative results, especially in patients with reduced renal function 1
Clinical Implications and Recommendations
Consider alternative protocols: When obstruction is suspected but initial F+20 diuretic renogram is negative or equivocal, consider using F+0 or F-15 protocols which have shown higher accuracy 3, 4
Use MAG3 over DTPA: MAG3 is preferred over DTPA for diuretic renography as it is more efficiently extracted by the kidney and provides better evaluation of washout, especially in patients with reduced renal function 1
Ensure adequate hydration: Proper hydration before and during the study is essential to maximize test accuracy 1, 5
Correlate with other imaging: Findings should be correlated with ultrasound, CT urography, or MR urography to improve diagnostic accuracy 1
Consider pressure-flow studies: In pediatric patients with equivocal diuretic renogram results, pressure-flow studies may provide more definitive assessment of obstruction 6