*Purpose: Pre-donation total kidney volume was shown to correlate with graft outcomes and long-term graft survival. However, only a few studies have studied the changes of the graft volume in the recipient, with conflicting results. We investigated variations in graft volume changes after kidney transplantation and their clinical outcomes.

*Methods: Between 2012 -2019 we retrospectively reviewed 40 kidney recipients who had an abdominal Computed tomography (CT) within the first year after kidney transplantation. Recipient kidney volume (RKV) was calculated and correlated with donor kidney volume (DKV) to calculate a graft volume change percentage (GVC) (GVC= DKV/RKV x 100). Patients were divided into Group 1 (GVC less than 150%) and Group 2 (GVC more than 150%). Estimated glomerular filtration rate (eGFR) was calculated at 1-, 3- and 6-months then yearly up to 8 years post-transplantation using the CKD-EPI formula. Other clinical outcomes including rejection, BK viremia and graft survival were correlated with the GVC.

*Results: The median donor age was 45 years (IQR: 37-53), median BMI was 27.3 (IQR: 23.7-29.5) and males were 42.5%. The median DKV was 171.5 cc (IQR: 150-190). Most of the allografts experienced progressive enlargement in the first year after transplant with a median RKV of 225 cc (IQR: 194-291) and a GVC of 135% (IQR: 120-165). Patients in Group 1 had a higher Median e-GFR compared to Group 2 on short and long term follow up (figure 2). Young donor kidney were more likely to be associated with a lower GVC (p=0.038).

*Conclusions: Graft kidneys are expected to enlarge in the first year after transplantation. A possible explanation is compensatory hypertrophy. However other possible reasons are hyperfiltration, inflammation, and edema. Our data suggest that more than 50% enlargement of the graft in the first year is associated with a lower GFR on short and long term follow up which might reflect a pathological process rather than compensatory hypertrophy. Young donor kidneys were more likely to have less than 50% enlargement in the first year post-transplant.

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