Diagnostic utility of anti-Mycobacteriumtuberculosis antibody ab905 for the diagnosis of extrapulmonary tuberculosis in archived tissue specimens, a cross-sectional study at Mbarara Regional Referral Hospital

Amadile Lawrence, Abraham Birungi, Hassan Wasswa, Charles Bagenda Nkubi, Richard Kasadha, Saphurah Nabaasa, Lauben Tibenderana, Jolly Lydia Ninsiima, Keneth Male, Sunday Afeku, Raymond Atwine, Yekosani Mitala, Frank Ssedyabane

Abstract:

Background: Diagnosing extrapulmonary tuberculosis (EPTB) poses challenges such as delayed diagnosis, missed diagnosis, and misdiagnosis of EPTB. Immunohistochemistry is believed to improve the accuracy of EPTB diagnosis in tissues fixed in formalin and embedded in paraffin.

Purpose: The primary objective of this study was to determine the sensitivity and specificity of anti-Mycobacterium tuberculosis antibody staining for diagnosing EPTB in tissue specimens.

Patients and methods: This was a cross-sectional study, and data were collected between June 2023 and November 2023, involving 87 archived tissue specimens from patients with clinical suspicion of EPTB. Demographic data were collected from pathology registers, and Hematoxylin and Eosin (H&E) and Ziehl Neelsen (ZN) staining and microscopy techniques were repeated to confirm the diagnosis of EPTB. A concentrated anti-Mycobacterium tuberculosis antibody (ab905, Abcam, Cambridge, UK), diluted (1:100) for immunohistochemistry. Indirect manual IHC technique was performed. ZN and/or histopathology were used as the component composite reference standard tests.

Results: The study population comprised of 87 tissue blocks. Lymph nodes constituted the majority (50/87, 57%) of specimens. Histopathologically, 52.9% (46/87) of the specimens had granulomatous inflammation suggestive of EPTB, whereas 47.1% (41/87) did not. Of the 87 specimens analyzed, 17 (19.5%) were positive using the ZN technique and 70 (80.5%) were negative. The sensitivity, specificity, PPV, and NPV of anti-Mycobacterium tuberculosis antibody staining were 74.5%, 80.0%, 81.4%, and 72.7%, respectively.

Conclusion: Based on the findings of our study, anti-Mycobacterium tuberculosis antibody ab905 staining is a valuable method for excluding or diagnosing EPTB in tissues. Prospective data collection using a monoclonal ab905 anti-Mycobacterial tuberculosis antibody and a more sensitive gold standard would negate the limitations of this study.

Contribution: Our study provides insight into the potential role of immunohistochemistry in the diagnosis of EPTB.

Keywords: Sensitivity; Specificity; Formalin-fixed paraffin-embedded; Hematoxylin & Eosin; Immunohistochemistry; Ziehl-Neelsen.