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). Ng was calculated as (Vv(glom/cortex) X 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%, Vcortex was 167 46 cm(3), V-g-W&G was 3.2 +/- 1.2 X 10(6) mum(3), and V-g-MPA was 3.3 +/- 1.0 X 10(6) mum(3). V-g-W&G in donor and recipient biopsies was not different (3.6 +/- 1.1 versus 3.2 +/- 1.2 X 10(6) mum(3)). Total glomerular number estimated by means of V-g-W&G (N-g-W&G) was 0.73 +/- 0.33 X 10(6) and by V-g-MPA (N-g-MPA) was 0.74 +/- 0.31 X 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.