Renal transplants increase in size and function in keeping with compensatory renal hypertrophy

To evaluate changes in allograft kidney length in renal transplant recipients and the relationship with estimated glomerular filtration rate (eGFR).

This single-centre retrospective study of renal transplant recipients was conducted at Flinders Medical Centre (FMC) from January 2007 to June 2020. Donor and recipient details, renal allograft length from transplant ultrasounds at 0, 1, 3, 6 and 12 months were collected. The association between compensatory renal hypertrophy (CRH) and eGFR and its magnitude was analysed using multivariate multilevel mixed-effects linear regression models.

A total of 183 renal transplant recipients were studied. 100 of 175 recipients (62.9%) demonstrated an increase in renal length defined as any increase in maximal longitudinal diameter on serial ultrasounds. Twenty-three recipients (13.1%) had no change in transplant length and 42 recipients (24%) had a decrease in length. The mean increase in kidney length over the first 12 months was 0.57 cm. Ninety of 156 (57.7%) recipients with a renal ultrasound within a month post-transplant demonstrated a mean increase kidney length of 0.3 cm. Multivariate analysis demonstrated that eGFR increased by 2.5 mL/min/1.73 m² (95% CI 0.72- 4.4; p = .006) with every 1 cm increase in kidney length. Absolute changes in kidney length did not demonstrate any statistically significant correlation with eGFR in both complete case and multiple imputation analysis.

An increase in transplant kidney length is common in renal transplant recipients and is associated with enhanced eGFR. However, further studies need to be performed to study the association of absolute change in kidney length and eGFR.