Serologic diagnosis of bone and joint tuberculosis by an enzyme-linked immunosorbent assay

Sera from patients receiving treatment for active bone and joint tuberculosis and sera from patients with inactive bone and joint tuberculosis were examined by an enzyme-linked immunosorbent assay for antibody to antigen 6, a homogeneous protein prepared from Mycobacterium tuberculosis strain H37Ra by immunosorbent affinity chromatography. Sera from 21 control subjects had a geometric mean titer of 1:6 with no difference between tuberculin purified protein derivative-positive and -negative patients. Sera from 20 patients with inactive disease had a geometric mean titer of 1:19. Fifteen patients receiving treatment for M. tuberculosis infection had a geometric mean titer of 1:179, which is significantly different from the geometric mean titers of both of the patients with inactive tuberculosis (P less than 0.001) and the control subjects (P less than 0.001). At a cut-off titer of 1:32, the sensitivity of the assay is 94% and the specificity for the control subjects and patients with inactive disease was 100%.