Measurement of glomerular volume in needle biopsy specimens

Background. Various methods have been used to determine mean glomerular volume, some requiring measurement of over 30 glomerular profiles for a. satisfactory estimate. Needle biopsies are useful diagnostically, but if small, provide insufficient tissue for the use of such methods. Methods. We performed glomerular volume measurements on renal biopsies from 10 normotensive, non-uraemic patients with Type 1 diabetes. Sections were taken at 10 mu m intervals through 10 glomeruli per biopsy and points landing on glomerular tuft counted under light microscopy. Volume was calculated from the measured cross-sectional area and known section thickness using the Cavalieri principle. Results. Estimating the volume of 10 glomeruli per biopsy gave an overall mean glomerular volume of 4.21 x 10(6) mu m(3) and standard deviation between patient means 1.23 x 10(6) mu m(3). Using a sample size of five glomeruli per biopsy only increased the standard deviation between patient mean values by 3%. Using sections taken at 20 mu m intervals made little difference to the mean glomerular volume and standard deviation estimates (MGV 4.20 x 10(6) mu m(3) +/- 1.24). Further increases in the sectioning interval resulted in an appreciable increase in the variance of the estimate. Conclusions. The results suggest that a satisfactory estimate of mean glomerular volume can be obtained from a sample size of five glomeruli per biopsy using a sectioning interval of 20 mu m. This represents a great saving in analysis time and effort, making widespread use of this method of glomerular volume measurement in renal disease more practicable, in both research and clinical settings.