How thick are the paraffin-embedded tissue sections routinely prepared in laboratory? A morphometric study using a confocal laser scanning microscope

In order to evaluate the differences between cut and measured thicknesses of formalin-fixed, paraffin-embedded tissue sections, formalin-fixed, paraffin-embedded blocks of liver tissue were prepared from four male Wistar rats, The sections were cut at preselected thicknesses of 3, 6, 9, 12, 15 and 18 mu m, and observed under confocal laser scanning microscopy. The maximum and minimum section thicknesses were measured using a vertically cut section image constructed by the software incorporated in the microscope, The surface of the section was not smooth but showed fine undulations in addition to a slight inclination, The mean and range of the section thicknesses measured were 4.3 +/- 1.3, 7.0 +/- 1.7, 9.8 +/- 2.1, 12.0 +/- 2.6, 14.1 +/- 3.0, and 17.7 +/- 3.8 mu m for the preselected cut thicknesses of 3, 6, 9, 12, 15 and 18 mu m. It is stressed that the evaluated parameters of the section (volume or surface densities) include standard errors of up to 10% caused by the differences between the cut and real thicknesses.