Diagnosis of kidney transplant obstruction using Mag3 diuretic renography

Kidney transplant obstruction (KTO) following renal transplantation remains an important reversible cause of allograft dysfunction, requiring prompt d iagnosis to prevent long-term graft damage. Although ultrasound can accurat ely diagnose renal transplant hydronephrosis, it cannot be used to assess i ts functional significance. We prospectively assessed the utility of techne tium-99m mercaptoacetyltriglycine (Tc-99m MAG3) diuretic renography for the diagnosis of allograft KTO, using standard visual and quantitative paramet ers, as well as calculated renal output efficiency (OE), which has been pos tulated to improve diagnostic yield. From a cohort of 45 renal transplant p atients, two subgroups were formed. The first group of transplant recipient s (n = 21) with stable function and no obstruction was used to derive norma l values for Tc-99m MAG3 scans. A second group of transplant recipients wit h acute renal dysfunction in whom KTO was clinically suspected was used to test the diagnostic utility of these derived values (n = 43 scans). KTO was diagnosed independently of the MAG3 scans by a fall in the serum creatinin e in response to renal pelvis urinary drainage. OE in 12 renal allografts w ith KTO was significantly reduced compared with 31 Tc-99m MAG3 scans withou t KTO (59.6 +/- 18.9 vs. 81.6 +/- 5.4%, p < 0.001). In KTO, the mean time o f isotope appearance in the bladder (time to bladder [TTB]) was extended co mpared with unobstructed allografts (7.9 +/- 4.1 vs. 3.6 +/- 1.5 min, p < 0 .001). Measurement of OE significantly improved the accuracy of diuretic MA G3 renography in the diagnosis of renal allograft KTO, especially when supp lemented by the TTB, parenchymal transit time and shape of the renogram cur ve. Ureteric obstruction of the kidney transplant can be diagnosed with an OE reduced to < 75% (sensitivity 92%, specificity 87%) and confirmed by iso tope hold-up in the pelvica-lyceal system. A normal or slowly declining ren ogram curve effectively excluded KTO (sensitivity of 96%, negative predicti ve value of 84%). A parenchymal transit time of > 5 min and a TTB of > 7 mi n both yielded a sensitvity of 92% and a specificity of 81%. In conclusion, MAG3 renography is a clinically useful investigation for the diagnosis of KTO.