Cytology is the study of individual cells and cytopathology is the study of individual cells in disease. Sampled fluid/ tissue from a patient is smeared onto a slide and stained (see techniques). This is then examined under the microscope by the anatomical pathologist to look at the number of cells on the slide, what types of cells they are, how they are grouped together and what the cell details are (shape, size, nucleus etc). This information is useful in determining whether a disease is present and what is the likely diagnosis.

Cytology is most often used as a screening tool to look for disease and to decide whether or not more tests need to be performed. An example of screening would be the investigation of a breast lump. In combination with examination by the clinician and imaging tests, a needle aspirate of the lump submitted for cytology will show whether the breast cells are suspicious for cancer or look bland/ benign. If they look suspicious, a core biopsy with a larger needle may be performed which takes more tissue, allowing for a definitive diagnosis to be made before deciding what type of surgery is required (local removal of the lump or removal of the whole breast).
 

Sampling techniques in cytology

Exfoliative cytology
This is the analysis of cells that are shed from body surfaces. Examples include the lining cells of the uterine cervix (mouth of the womb) and of the bladder. The analysis of cells from the cervix is a minimally invasive procedure called a cervical or Pap smear. This involves the insertion of a speculum into the vagina to allow the clinician to directly view the cervix. The cervix is then gently scraped to retrieve cervical cells which are smeared directly onto glass slides at the bedside and submitted to a laboratory for examination.

Aspiration cytology
The analysis of cells from within a mass or organ. This involves a more invasive sampling procedure called Fine Needle Aspiration (FNA). A needle is inserted into the area of the body being examined, sometimes with the use of imaging (e.g. ultrasound or CT scan) to ensure that the suspicious area is being sampled. This procedure may be performed after injection of local anaesthetic to numb the skin, or even under light sedation if involving a deep organ or tissue. The cells retrieved are expressed onto a slide and prepared in a similar way to the cervical smear. If fluid is aspirated (e.g. within from a thyroid cyst), it may first be spun by a centrifuge so that the cell-containing sediment collects at the bottom of the test tube, allowing the best material to be sampled for examination.
 

Examining cytology material

The most common samples in cytology are exfoliative, including cervical smears (Pap smears), urine and sputum. These are usually screened by trained cytotechnicians or, in some laboratories, computerised automated systems, to look for any suspicious cells. These suspicious samples are then forwarded on to a pathologist for further microscopic examination and final diagnosis. Aspirated material is usually viewed by a pathologist directly.

Special stains are performed to highlight the cells and background material on the slide, in a similar way to histopathology sections.