Detecting extrapulmonary tuberculosis using immunohistochemistry with anti-Mycobacterium tuberculosis antibody ab905; a cross-sectional study at Mbarara Regional Referral Hospital

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. 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 performed on sections from the tissue blocks to confirm the diagnosis of EPTB. A concentrated anti- Mycobacterium tuberculosis antibody (ab905, Abcam, Cambridge, UK), diluted (1:100) for immunohistochemistry (IHC) was used. 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.