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Cytopathology is a branch of pathology that studies and diagnoses diseases on the cellular level. The most common use of cytopathology is the Pap smear, used to detect cervical cancer at an early treatable stage.

Two methods of collecting cells for analysis are:

1. Exfoliative Cytology – Cells are extracted from fluid shed into the body cavities. For example, in pleural fluid, ascitic fluid, or in the case of the Pap smear, cells scraped from the cervix.
2. Fine Needle Aspiration Cytology or Needle aspiration biopsy – An 18 to 27 gauge (most commonly 23-25) needle attached to a 10 cc syringe is used to aspirate (pull out) cells from lesions or masses in various organs of the body by application of negative pressure (suction). FNAC can be done directly on a mass in superficial regions like the neck, thyroid or breast; or it maybe be assisted by ultrasound or CAT scan. FNAC, while poorly developed in the USA, is widely used in Europe and India. Being a skill dependent procedure, the success rate may vary. If performed by pathologist or as team with pathologist-cytotechnologist, the success rate of proper diagnosis is superior. The two countries with the most advanced FNAC services are Sweden (Karolinska hospital performs about 11 thousand annual aspirates), and Slovenia (Institute of Oncology performs about 10 thousand annual aspirates). The highest volumes in USA are encountered at Emory University Hospital in Atlanta GA, and MD Anderson Hostpital in Houston, TX, each contributing no more than 4 thousand aspirates per year.

Fine needles are 23 to 27 gauge. Needle diameters and color codes for 23G, 25G and 27G are as follows, respectively: 0,6 mm/Blue-dark, 0,5 mm/Orange, and 0,4 mm/Grey. If a cell-block preparation is indicated, after obtaining diagnostic cytology smears, a wider gauge needle, up to 18 gauge, may be used.

• Cellular pathology