A cytology test, also known as cytopathology, is a common diagnostic procedure used to examine individual cells or small clusters of cells under a microscope to identify disease. This method allows medical professionals to look for cellular changes that may indicate infection, inflammation, or the presence of cancer. Cytology is often preferred over a traditional biopsy, which examines a piece of tissue, because it requires a much smaller sample and is less invasive.
The process involves cell collection, specialized laboratory preparation, and a detailed report from a pathologist. Cytology is used both for screening healthy individuals and diagnosing specific conditions.
Methods for Sample Acquisition
The first step in any cytology test involves collecting the cells from the specific area of the body being examined. The collection method depends entirely on the location of the cells and whether they are naturally shed, suspended in fluid, or part of a solid mass. There are three general approaches used to gather these microscopic samples.
Exfoliative cytology involves collecting cells after they have naturally shed or are gently scraped from a surface. The Pap smear, which collects cells from the cervix using a brush or swab, is a prime example. Other procedures include scraping the skin, using a brush during an endoscopy to collect cells from the respiratory or digestive tract, or collecting body secretions like breast discharge.
Fluid cytology focuses on collecting cells suspended within bodily fluids. This involves collecting urine, cerebrospinal fluid, or fluid accumulated in body cavities, such as pleural fluid from the lungs or ascitic fluid from the abdomen. These samples are typically collected in a sterile container and sent immediately to the laboratory for processing, sometimes with a preservative added to maintain cell integrity.
When cells need to be collected from a deeper, solid mass or organ, Fine Needle Aspiration (FNA) is used. This technique involves inserting a very thin, hollow needle into the mass to draw out a small sample of cells and fluid. FNA is often guided by imaging like ultrasound or CT scans, though providers may simply feel surface masses to guide the needle. This is generally a quick procedure that aims to obtain enough material for diagnosis with minimal discomfort.
Preparing Samples for Microscopic Review
Once the cells are collected, they must be processed in the laboratory to make them viewable under a microscope, a process called cytopreparation. Fixation stabilizes the cells and prevents them from degrading or changing shape. For samples collected directly onto a slide, such as an FNA or a scrape, the material is immediately immersed in a fixative, usually 95% ethyl alcohol, or sprayed with a commercial fixative while the smear is still wet.
Fixation prevents air-drying artifacts, which can distort cell shape and make accurate diagnosis difficult. Some samples, especially those collected via FNA, may be air-dried instead and stained using a different method, such as a Romanovsky stain like Diff-Quik. Fluid samples often require centrifugation to concentrate the small number of cells before they can be placed onto a slide.
After fixation, the cells are stained with colored dyes to make their internal structures visible. The Papanicolaou stain (Pap stain) is the standard method for many cytology specimens because it uses multiple colors to highlight the cell nucleus, cytoplasm, and background elements. This differential staining allows the cytologist to clearly distinguish between normal and abnormal cellular features, such as variations in nuclear size or chromatin pattern.
Once the slide is prepared and stained, it is ready for screening, often performed by a specialized cytotechnologist. The technologist systematically examines the entire slide under the microscope, looking for any cellular changes or abnormalities. If suspicious findings are identified, the slide is then passed to a pathologist—a medical doctor trained in diagnosing disease by examining cells and tissues—for final review and interpretation.
Understanding the Pathologist’s Report
The final stage of the cytology process is the creation of the diagnostic report by the pathologist, which communicates the findings to the ordering physician. This report typically categorizes the cellular findings using standardized terminology. A result of “negative” or “benign” means that no signs of disease or malignancy were found in the sample.
A common finding is “atypical,” meaning the cells show changes that deviate from a normal appearance but are not clearly malignant. Atypia can be caused by various factors, including inflammation, infection, or normal aging, and does not necessarily indicate cancer. In these cases, the report often suggests follow-up testing, such as a repeat cytology test or further imaging, to monitor the cells.
If the pathologist identifies features that strongly suggest malignancy, the report will often use terms like “positive for malignant cells” or “carcinoma.” The criteria for malignancy involve observing specific cellular changes, such as a high nuclear-to-cytoplasmic ratio, variation in cell size, and abnormal nuclear shapes. Because cytology provides a small sample of cells, the report may recommend a surgical biopsy, which examines a larger piece of tissue, to confirm the diagnosis and determine the extent of the disease.