Cytology

Cytology is a branch of pathology that studies individual cells and their features, including morphology, structure, and function, to diagnose disease. It encompasses the preparation and examination of cells obtained from tissues, fluids, or washes, as well as the analysis of cell samples from fine-needle aspirations. Cytology emphasizes cellular detail rather than tissue architecture, contrasting with histology, which analyzes intact tissue.

Common cytologic specimens include exfoliative samples such as cervical smears, sputum, urine, and pleural or peritoneal fluids, as well as aspirates obtained by fine-needle aspiration from masses or organs. In some settings, rapid on-site evaluation is performed to assess specimen adequacy. Samples are fixed and stained to reveal cellular morphology. Routine stains include Papanicolaou and Romanowsky-type stains (Diff-Quik, Giemsa). Techniques such as cytospin and liquid-based cytology improve cell preservation and slide quality. Cytotechnologists screen slides and cytopathologists render final interpretations.

Cytology plays a critical role in cancer screening, diagnosis of neoplasia and infections, cytodiagnosis of effusions, and monitoring of treatment response. It can provide rapid preliminary diagnoses and is less invasive than many surgical biopsies, but it has limitations, including lack of tissue architecture and sampling errors; results are interpreted in the clinical context and often correlated with histology and imaging.

Advances in cytology include molecular testing on cytology specimens and the use of immunocytochemistry for lineage, markers, or infection. The discipline is supported by cytotechnologists and cytopathologists who specialize in evaluating cell morphology.