Introduction: Kidney graft resistance index (RI) measured by vascular Doppler sonography has been associated with systemic and local vascular factors with negative effects on the kidney function evolution, which is why RI may be a prognostic factor of graft function.

Objectives: To determine the relation between RI and factors influencing the graft function, and whether there is an association between increased RI and a worsened evolution of kidney function.

Methods: Vascular Doppler ultrasound was performed in 119 stable living- and deceased-donor renal transplant patients more than 3 months after transplantation. Their IR was measured initially at a check-up (T0) and then two years later (T1). RI was analyzed in a bimodal way (RI <0.8 and ≥0.8) and by tertiles (<0.68, 0.69-0.81, >0.81). Creatinine (Cr), glomerular filtration (GF) using the CKD-EPI equation, and proteinuria were also assessed upon measuring RI: (T0) and after 2 years (T1). The relationship with other variables, such as age, diabetes (DM), delayed graft function (DGF), was analyzed and, during those two years, the presence of rejection, recurrent urinary tract infections (rUTIs) and progression to dialysis or death was described.

Results: Male 44%; average age 48 years (38-57); DM 17%; DGF 59%. Kidney function at T0 was: Cr 1.3 (1.1-1.7), GF 54 (40-65), proteinuria 0.22 (0.14-0.4) and at T1: Cr 1.31 (1.07-1.7), GF 56 (40.3-69.8), proteinuria 0.24 (0.14-0.4). Progression to death 8%, dialysis 9%, rejection 8%, UTI 8%.The bimodal analysis showed a significant relation between RI >0.8 and older age (p=0.001) and DM (P=0.004). The tertile analysis indicated a significant relation with older age (p=0.001), increasing when comparing tertiles <0.68 and >0.81 (p=0.0001). There was also a significant association between DM and the highest RI tertile (p=0.01). Both the bimodal and the tertile analyses showed increased Cr levels and decreased GF rates in RI >0.8, but no significant relation. There was no significant difference in Cr, GF and proteinuria between T0 and T1 either. There was no relation with sex, DGF, progression to death, dialysis, rUTI or rejection.

Conclusion: An association between increased RI and older age and DM, as reported in other studies, is found. Such variables are directly related to vascular factors, such as increased pulse pressure and microvascular injury, elements known to impair graft function in the long term. Even though this study shows a tendency to a worsened kidney function with a high RI, its relation is not significant and no difference is found after 2 years. Further studies with greater time variation are required to assess these parameters.