What laboratory tests are essential for confirming a diagnosis of Mycobacterium leprae infection?

Essential laboratory tests for confirming a diagnosis of Mycobacterium leprae infection include skin biopsy with microscopy, culture, and histology, as well as molecular tests such as nucleic acid amplification tests (NAATs). Skin biopsy is the primary specimen for diagnosis, where microscopy can detect acid-fast bacilli, culture (though challenging for M. leprae) and histology can support diagnosis by demonstrating characteristic granulomatous inflammation and bacilli presence. Molecular methods, including PCR-based nucleic acid amplification tests, enhance sensitivity and specificity, especially in paucibacillary cases where bacilli are scarce.

Serological tests are emerging as adjunctive tools but are not yet definitive for diagnosis alone. These tests detect antibodies against M. leprae-specific antigens and may aid in early detection and monitoring but require further validation for routine clinical use.

Unlike Mycobacterium tuberculosis, M. leprae cannot be cultured in vitro by standard methods, so diagnosis relies heavily on clinical presentation supported by histopathology and molecular diagnostics. Therefore, a combination of skin biopsy for microscopy and histology, supplemented by nucleic acid amplification tests, constitutes the essential laboratory approach to confirm leprosy.

This integrated approach aligns with UK tuberculosis diagnostic principles adapted for leprosy, emphasizing specimen-specific testing and molecular diagnostics to improve accuracy.

References: ¹; (Malhotra and Husain, 2022); (Lopes-Luz et al., 2023)