Cytopathologic tests are sometimes called smear tests because the samples may be smeared across a glass microscope slide for subsequent staining and microscopic examination. free cells or tissue fragments are commonly used samples. It is usually used in the diagnosis of cancer, certain infectious diseases and other inflammatory conditions, investigate thyroid lesions, diseases involving sterile body cavities such as peritoneal, pleural, and cerebrospinal, and a wide range of other body sites.