Laboratory diagnosis of leprosy is primarily based on clinical signs and symptoms. Skin and nasal smears can be taken from lesions to look for acid-fast Mycobacterium leprae bacteria under microscopy. Biopsies of infected skin or nasal tissue can also be analyzed with acid-fast staining, culturing, or PCR to confirm the presence of M. leprae DNA. Classification of leprosy type is aided by the Lepromin skin test response and lymphocyte proliferation assays, which indicate level of cell-mediated immunity toward M. leprae.