Significance of early tubular extraction in the first minute of Tc-99m MAG3 renal transplant scintigraphy

Renal transplant perfusion curves obtained using Tc-99m MAG3 differ from those with Tc-99m DTPA. The perfusion curve can be divided into a first phase (up to the first-pass peak) and a second phase (the curve after the initial peak). The second phase of the MAG3 perfusion curve is usually ascending in contrast to the descending Tc-99m DTPA curve. This ascending MAG3 curve reflects early tubular extraction of MAG3, However, the second phase of the MAG3 curve is sometimes flat or descending. We hypothesized that a flat or descending curve reflects poor early tubular extraction acid therefore graft dysfunction. Ninety-two studies of 59 renal transplant patients were retrospectively reviewed. The second phase of the perfusion curve was visually classified as ascending, flat, or descending. 77.2% of studies had ascending curves, 16.3% flat curves, and 6.5% descending curves. A descending curve had a positive predictive value (PPV) of 100% for medical graft dysfunction, while a flat curve had a PPV of 93.3%. A nonascending second phase curve was specific (96.4%) but not sensitive (33.9%) for graft dysfunction. Patients with acute tubular necrosis were not significantly more likely to have a nonascending curve than those with acute rejection. There was no significant difference in creatinine level between patients with medical graft dysfunction and ascending vs. nonascending curves. A nonascending second phase Tc-99m MAG3 perfusion curve is predictive for graft dysfunction. An ascending curve is nonspecific and can be seen in both normally and poorly functioning grafts.