Genkins et al [14] found a sensitivity of 9%, a specificity of 91%, a PPV of 29%, and an NPV of 70% using an RI cutoff of 0.90 for the diagnosis of allograft rejection. Previous studies have shown that renal arterial RI is useful in predicting graft survival [15], especially when using a lower RI cutoff of 0.8. Radermacher et al [15], using a cutoff of 0.80 at 3 months after transplantation, found that 47% of patients with RI >0.80 developed chronic allograft nephropathy (CAN), compared to 9% of patients with RI <0.80. McArthur et al [16] found that both RI and pulsatility index measured between week 1 and 3 months significantly correlated with the 1-year estimated glomerular filtration rate. Although an RI >0.80 was initially thought to correlate with allograft dysfunction, a recent study by Naesens et al [17] raises doubt on this theory. Their single-center prospective study analyzed RI at the time of protocol- specified renal allograft biopsies in addition to patients with graft dysfunction. Patients with RI >0.80 did have 4.12 times higher mortality at 24 months than those <0.80, but their need for dialysis did not differ. The RI was significantly higher at the time of biopsy performed in patients with graft dysfunction, but changes in the RI did not reflect changes in histologic features when biopsies were performed at protocol-specific time points. The authors surmised that these changes did not reflect an underlying intrarenal disease process but were related to patient age and central hemodynamic factors. This complex interaction of coexisting factors in renal transplants makes the interpretation of Doppler parameters difficult. Despite this recent study, US with Doppler imaging remains the first-line imaging in the early post-transplantation period as it establishes a baseline for future comparisons.
Renal Transplant Dysfunction. Genkins et al [14] found a sensitivity of 9%, a specificity of 91%, a PPV of 29%, and an NPV of 70% using an RI cutoff of 0.90 for the diagnosis of allograft rejection. Previous studies have shown that renal arterial RI is useful in predicting graft survival [15], especially when using a lower RI cutoff of 0.8. Radermacher et al [15], using a cutoff of 0.80 at 3 months after transplantation, found that 47% of patients with RI >0.80 developed chronic allograft nephropathy (CAN), compared to 9% of patients with RI <0.80. McArthur et al [16] found that both RI and pulsatility index measured between week 1 and 3 months significantly correlated with the 1-year estimated glomerular filtration rate. Although an RI >0.80 was initially thought to correlate with allograft dysfunction, a recent study by Naesens et al [17] raises doubt on this theory. Their single-center prospective study analyzed RI at the time of protocol- specified renal allograft biopsies in addition to patients with graft dysfunction. Patients with RI >0.80 did have 4.12 times higher mortality at 24 months than those <0.80, but their need for dialysis did not differ. The RI was significantly higher at the time of biopsy performed in patients with graft dysfunction, but changes in the RI did not reflect changes in histologic features when biopsies were performed at protocol-specific time points. The authors surmised that these changes did not reflect an underlying intrarenal disease process but were related to patient age and central hemodynamic factors. This complex interaction of coexisting factors in renal transplants makes the interpretation of Doppler parameters difficult. Despite this recent study, US with Doppler imaging remains the first-line imaging in the early post-transplantation period as it establishes a baseline for future comparisons.