Cytology & Cytodiagnosis
Cytology is the scientific study of the structure, function, and behavior of individual cells, focusing on their characteristics to understand various cellular processes. Cytodiagnosis, on the other hand, applies cytology as a diagnostic tool to identify abnormalities in cells that may indicate disease. This process involves using well-established, highly specific stains and protocols to enhance the visibility and identification of abnormal cell features under a microscope. Cytodiagnosis plays a crucial role in both gynecological and non-gynecological fields, where samples are carefully examined for the presence of malignant, premalignant, or other disease-related cellular changes, helping in the early detection of conditions like cancer and other cell-related disorders.
Overview
Cytologic Sampling
In cytodiagnosis, cells are extracted from tissue or sample fluid and transferred to a cytological slide for staining and evaluation. Specimens such as sputum, urine, body cavity effusions, and lavage material are centrifuged, with the sediment smeared onto slides. Fine-needle aspiration biopsy (FNAB) material from various body parts, including the breast, thyroid, and lymph nodes, is similarly smeared onto slides for examination. Depending on the staining method, the samples are either fixed immediately or air-dried prior to staining.
Fixation for Cytology
Fixation is crucial for accurate cytological diagnosis. Specimens must be fixed immediately to preserve cell structure and prevent drying or shrinking. The traditional method involves immersing the slide in 96% ethanol for 30 minutes, but a more efficient approach uses a spray fixative. Spray fixatives, usually aqueous-alcoholic solutions containing polyethylene glycol (PEG), are suitable for a wide range of cytological materials, especially those stained by the Papanicolaou method.
Cytodiagnosis Staining Methods
The choice of staining technique depends on the specimen type and the investigator’s preference. Papanicolaou’s staining method is commonly used for both gynecological and non-gynecological samples, including sputum, cerebrospinal fluid, synovial fluid, and urine. Giemsa’s stain is frequently used for FNAB specimens from lymph nodes, while Pappenheim’s stain is applied to urinary sediments, effusions, bronchial lavage, and FNAB material. Wright’s stain is used in hematology to differentiate blood cell types. Staining processes often include alcohol/xylene dehydration, clearing, and mounting. Automated systems are also available for processing large numbers of samples.
Cytodiagnostic Interpretation
Cytodiagnosis involves microscopic examination of the prepared and stained samples, making it suitable for high-volume screenings such as cervical screenings. The results of cytological investigations are directly related to the location from which the sample was collected. To ensure accurate diagnoses, strict control over sampling, fixation, staining, and interpretation is necessary. Diagnostic cytology is especially important for detecting early disease changes (sensitivity) while minimizing false positives (specificity). Alongside imaging techniques such as X-ray, CT, ultrasound, and PET, cytology plays a critical role in diagnostics.