Figure 1. Different methods for estimation of nephron number.

A) Disector/Fractionator method requires extensive sectioning of the whole kidney. In a series of subsampling steps, a known fraction of tissue is processed and sectioned. Glomeruli are then counted using section pairs (disector principle). In a schematic example of 2 pairs, only the three glomeruli in blue color indicated with arrows would be counted. Finally, total number of counted glomeruli is multiplied with an inverse of known sampling fractions to obtain the total number of glomeruli in the whole kidney. B) Measured GFR, renal plasma flow and plasma oncotic pressure are used to estimate the whole kidney Kf. Following kidney biopsy, an ultrastructural analysis of glomeruli provides estimates of filtering surface area and hydraulic permeability, used to calculate single nephron Kf. The number of functional glomeruli is then calculated by dividing whole kidney Kf by single nephron Kf. C) Semi-automated segmentation of predonation CT scans provides measure of cortical volume. A time zero biopsy is performed following kidney implantation, and Weibel and Gomez stereology models are used to estimate volumetric glomerular density. A product of cortical volume and volumetric density provides the total number of glomeruli.