Renal output efficiency and normalized residual activity examined by technetium-99m-DTPA renography have by far greater specificity to diagnose obstructive disease as compared to other conventional parameters of the renogram. First such study of output efficiency.

OBJECTIVE

The aim of this study was to assess the diagnostic ability of renal output efficiency (OE), normalized residual activity (NORA) and conventional interpretation of the diethylene triamine pentaacetic acid (Tc-DTPA) diuretic renogram (CIR) in diagnosing urine flow obstruction.

SUBJECTS AND METHODS

Group A consisted of 73 obstructed kidneys and Group B of 80 kidneys with dilated upper urinary tract. Forty eight kidneys were examined as the control Group C. A 40min acquisition with 240 of 10sec images was applied. Furosemide was administered after 20min (F+20). Post-void image was acquired at 50min. Output efficiency was calculated at 20min (OE) and 20min after furosemide test (OE) and NORA at 20min (NORA) and on the post-micturition acquisition (NORA).

RESULTS

Both the above parameters (OE and NORA) had high sensitivity (92% and 97%), specificity (99% for both) and accuracy (95% and 98%) in differentiating between obstructed and dilated unobstructed kidneys. The test of NORA correctly reclassified 40 out of 41 indeterminate or false positive results of the conventional interpretations of renograms (CIR) as obstructed (12 cases) or dilated (28 cases). Cut-off values for obstruction were <80% and ≥0.23 for OE and NORA, respectively. Compared to CIR, both parameters showed better specificity, especially NORA.

CONCLUSION

Factors of OE and especially NORA of the renogram by Tc-DTPA were able to diagnose urine outflow obstruction better than CIR. Specifically, these factors well differentiated obstruction from urinary tract dilatation.