Estimation of Total Glomerular Number in Stable Renal Transplants

. Glomerular number (N g ) is considered a major determinant of renal function and outcome. In the dog, it has been shown that Ng can be estimated with reasonable precision in vivo by means of a renal biopsy and magnetic resonance imaging (MRI). Thus, this method was applied to study anatomoclinical correlations in stable human renal transplants. Thirty-nine stable renal transplants were included. A protocol renal allograft biopsy was done at 4 mo. Biopsies were evaluated according to Banff criteria. Glomerular volume fraction (Vv glom/cortex ) was measured by means of a point-counting method, and mean glomerular volume (V g ) was estimated by means of Weibel and Gomez (V g -W&G) and maximal profile area (V g -MPA) methods. MRI was used to estimate renal cortical volume (V cortex ). N g was calculated as (Vv glom/cortex × V cortex )/V g . GFR was estimated by the inulin clearance. Ten age-matched donor biopsies served as controls for V g . Histologic diagnosis was as follows: normal ( n = 20), borderline ( n = 7), acute rejection ( n = 1), and chronic allograft nephropathy ( n = 11). Vv glom/cortex was 3.4 ± 1.1%, V cortex was 167 ± 46 cm 3 , V g -W&G was 3.2 ± 1.2 × 10 6 μm 3 , and V g -MPA was 3.3 ± 1.0 × 10 6 μm 3 . V g -W&G in donor and recipient biopsies was not different (3.6 ± 1.1 versus 3.2 ± 1.2 × 10 6 μm 3 ). Total glomerular number estimated by means of V g -W&G (N g -W&G) was 0.73 ± 0.33 × 10 6 and by V g -MPA (N g -MPA) was 0.74 ± 0.31 × 10 6 . A positive correlation between GFR and N g -W&G ( r = 0.47, P = 0.002) was observed. Furthermore, the older the donor, the higher V g -W&G ( r = 0.37, P = 0.01) and the lower N g -W&G ( r = −0.40, P = 0.01). Total glomerular number can be estimated in stable renal allografts by means of a renal biopsy and MRI. Our data show that N g depends on donor age and positively correlates with GFR. E-mail: 28383xfo@comb.es