Does delay in fixation affect the number of mitotic figures in processed tissue?

The effect of delay in fixation on the number of mitotic figures in tissues has received little attention, and previous studies have reached differing conclusions. The numbers of mitotic figures in the normal mucosa of six colectomy specimens were counted with delays in fixation of 30 minutes, one hour, two hours, three hours and six hours for samples from each specimen. The numbers of mitotic figures were counted in 50 whole crypts in each specimen by two observers. All phases of mitosis were counted. The number of observable mitotic figures declined by about 30% with a delay in fixation of two hours and by 50% with a delay of six hours. This observation has important implications for the handling of surgical specimens.