Cytology is focused on studying cells, their structure and intracellular processes. Cytological examination evaluates samples that include various cells but not pieces of tissue.
Cytology allows us to diagnose many diseases that are accompanied with pathological changes within cells. This is the biggest difference from histology, which uses a whole tissue sample. Histology is more reliable as it allows us to study the microscopic architectonics of the tissue, but cytology may it is sometimes difficult to obtain a high-quality sample for histological examination.
The principle of sampling cytological material aims to obtain multiple individual cells. T achieve this, we can smear cells from mucosal surfaces (e.g. endometrial cervix), fill a hollow organ with fluid that is later aspirated (bronchoalveolar lavage performed during bronchoscopy) or aspirate a sample of fluid, which is accumulated in a body cavity (pleural effusion, ascites). It is also possible to perform cytology of urine as a part of urinalysis.
After obtaining the sample, it is distributed on a glass slide, dyed with special dyes and examined under a microscope. The examining physician tries to find any cells in the sample, describe them and evaluate their attributes. It is especially important to confirm any cellular abnormalities that may be related to precancerous conditions or malignant diseases. These pathological findings include abnormal shape and size of cells, shape of cell nuclei, abnormal number of nuclei in a cell, the amount of captured cell divisions and others. In ideal case, the doctor is able to determine whether the cells in the examined sample are precancerous or belong to a tumor. However, it is not only about cancers, large number of white blood cells is related to inflammatory disease, large number of erythrocytes confirms bleeding, etc.
It is usually easy to obtain a sample, the examination is quite quick and its price is relatively low. However, it is necessary to again repeat that cytology is not considered to be fully equivalent to histology and negative cytological examination does not exclude the presence of a pathology.