Methods for estimating the volume of individual glomeruli

Background. The Cavalieri and maximal planar area (MPA) methods are commonl y used to measure the volume of individual glomeruli. Previous studies have suggested that the MPA method, which is less laborious, yields values that are much greater than those obtained by the Cavalieri method. The current study re-examined the relationship of MPA and Cavalieri values for glomerul ar volume in humans and rats. Methods. Both methods were used to measure the volume of 1201 glomeruli fro m 58 humans and 281 glomeruli from 15 rats. Tissue was embedded in Epon. Fu rther mathematical analysis was performed to assess the extent to which dev iation of glomeruli from spherical shape affects the relationship of values obtained by the MPA and Cavalieri methods. Results. MPA values exceeded Cavalieri values by an average of only 14 +/- 22% in humans and 6 +/- 16% in rats. The relationship of MPA to Cavalieri v alues was similar in individual humans and rats, with widely varying values for average glomerular volume. Neither the development of sclerosis nor th e loss of any connection to a tubule affected the relationship of the MPA a nd Cavalieri values for the volume of individual glomeruli. Mathematical an alysis showed that MPA values would not exceed Cavalieri values if glomerul i had ellipsoidal rather than spherical shape. Conclusion. Similar values for glomerular volume are obtained using the Cav alieri and MPA methods in humans and rats.