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 shed in the vagina.

2) Fine Needle Aspiration Cytology (FNAC) - A 18 to 20 gauge needle attached to a 10cc 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.