Estimating mean glomerular volume using two arbitrary parallel sections

The most reliable method for estimation of mean glomerular volume (MGV), the disector/Cavalieri method, is technically demanding and time consuming. Other methods suffer either from a lack of precise correlation with the gold standard or from the need for a large number of glomeruli in the sample. Here, a new method (the 2-profile method) is described; it provides a reliable estimate of MGV by measuring the profile area of glomeruli in two arbitrary parallel sections. MGV was estimated in renal biopsies from 16 diabetic patients and 13 normal subjects using both the Cavalieri and the 2-profile methods. The range of individual glomerular volumes based on the Cavalieri measurements was 0.31 to 4.02 × 10⁶ μm³. There was a high correlation between the two methods for MGV (r = 0.97; P < 0.0001). However, the 2-profile method systematically overestimated MGV (P = 0.0005, paired t test). This overestimation was corrected by introducing a multiplication factor of 0.91, after which statistical criteria of interchangeability with the Cavalieri method were met. The optimal distance between two sections was determined as 20 μm with a coefficient of variation of 7.4% in repeated measurements of MGV. On the basis of findings that values for MGV stabilize after ten glomeruli are measured by the disector/Cavalieri method, it was determined that the accuracy of MGV by the 2-profile method obtained by eight glomeruli was less than 7% different from ten in all cases. Thus, the 2-profile method is a practical alternative to the disector/Cavalieri method for estimating MGV, especially in small samples and blocks with limited residual tissue.