Q. Is ELISA for TB a confirmatory test for bone tuberculosis too?
No. ELISA for TB is not a confirmatory test for TB, and in fact has little relevance in diagnosis, being a poor diagnostic modality for TB - having a low sensitivity and specificity.
Since TB is endemic in India, most of us have been exposed to TB bacilli at some time in our childhood and consequently would have some titre of IgG antibodies against TB bacilli. IgM antibodies, in high titre, usually develop in cases with a history of recent exposure to TB bacilli, but indicate exposure, but not disease.
Bone TB can be diagnosed by imaging tests (X-ray. CT scan, MRI) coupled with fine needle aspiration of any collection followed by microbiology tests (AFB smear microscopy, AFB culture and ST) and molecular tests (PCR, RT-PCR, NASBA, etc)
A chest X-ray, followed by sputum microscopy and culture for TB bacilli, are better investigations for diagnosing pulmonary TB, which is the commonest form of TB, and might be associated with bone TB.