The significance of mycobacterium tuberculosis antibody, antigen 60 IgG in patients with abnormal chest radiography.

Background: The identification of acid-fast bacilli (AFB) in sputum or tissue is the definite diagnosis of tuberculosis. However, this method of diagnosis is restricted by certain limitations. The serologic diagnosis of tuberculosis has been used for a long time. The aim of this study was to determine the sensitivity and specificity of Antigen 60 (A60) immunoglobulin G (IgG) in patients with abnormal chest radiography and to assess its application in the serologic diagnosis of pulmonary tuberculosis.

Methods: Data on patients who had been diagnosed using results of culture and pathology as having active pulmonary tuberculosis (N=178), other non-tuberculosis pulmonary disease (N=34), or no pulmonary disease (N=117) was collected from January 2001 through December 2002. The data of A60 IgG using enzyme-linked immunosorbent assay (ELISA), chest radiography, tuberculosis culture and pathology were obtained retrospectively. The cutoff value of A60 IgG was chosen according to a receiver operating characteristic (ROC) analysis. The sensitivity, specificity, positive predictive value, negative predictive value and likelihood ratio for positive and negative test were determined.

Results: The chosen cutoff value of 261.2 units defined the sensitivity (49.4%) and specificity (79.5%) of the test. The positive predictive value and likelihood ratio were 95.7% and 4.20, respectively, for patients with abnormal chest radiography and 88.2% and 2.97, respectively, for patients with abnormal chest radiography and negative AFB in sputum smear.

Conclusions: Because of the high positive predictive value and likelihood ratio, a positive A60 IgG test in the presence of an abnormal chest radiography can help make an accurate clinical diagnosis of pulmonary tuberculosis.