As with any unbiased stereological procedure, the sampling parameters should be dictated by the distribution of the cell population. For very sparsely distributed populations, it is expected that a higher percentage of the tissue will need to be sampled in order to achieve an acceptable precision than would be necessary for a cell type which is more numerous. Depending on how sparse the population is, it’s possible that 100% of the cross-sectional area will need to be sampled, and each counting frame will always be adjacent to other counting frames. It is OK to scan for the rare cell type at a lower magnification for efficiency, but when you spot one, go back up to the oil lens to check if the leading edge of the particle is in the disector.
This FAQ comes from stereology.info, our curated collection of information and references regarding the use of stereology in the biological sciences. Feel free to review the other FAQs there as well. We hope this thread will spark some in-depth discussion on stereology!