FNAC (Fine Needle Aspiration Cytology) can be used to test for a variety of diseases and conditions. It is commonly used to investigate and diagnose both benign and malignant conditions in various organs and tissues, including breast lumps, thyroid nodules, lymphadenopathy, liver lesions, and more. FNAC can aid in diagnosing infections, inflammations, benign tumors, primary and metastatic cancers, and certain autoimmune conditions. The specific disease or condition being tested for depends on the site and characteristics of the lesion or mass under investigation.