Background: For early diagnosis of tuberculosis (TB), especially in the patients without adequate sputum specimens for examination, we found a simple, rapid and inexpensive method among many current available diagnostic tools, the enzyme-linked immunosorbent assay (ELISA). To investigate the diagnostic effectiveness of this method, we applied ELISA for detection of antigen 60 IgG and IgM as well as antigen 38 IgG antibodies at Chang Gung Memorial Hospital from April 1995 through June 1996.
Materials and methods: Sixty-seven patients were enrolled and divided into 3 groups, Group A (n = 24), patients with positive sputum acid-fast stain; Group B (n = 18), patients with lung cancer and negative sputum acid-fast stain; and Group C (n = 25), patients with chest roentgenogram (CXR) which were suggestive of TB but with negative acid-fast stain results or no sputum for examination.
Results: For the A60 IgG antibody, we found a sensitivity rate of 91.7% for Group A and Group B, and 85.7% for Group C as well as an overall sensitivity of 89.5% but with lower specificity. For the A60 IgM antibody, a lower sensitivity (37.5%, 14.3%, 28.9%, respectively) was found but with higher specificity. For the A38 IgG antibody, we found a lower sensitivity (40%, 11.1%, 31%, respectively) but with higher specificity (100%, 71.4%, 90%, respectively).
Conclusion: With a high sensitivity but low specificity for diagnosis of TB, A60 IgG ELISA could be used as a rapid, simple screening test for patients with results suggestive of TB, especially in those who had no sputum or had negative sputum acid-fast stain results. Otherwise, A60 IgM or A38 IgG ELISA, with a high specificity, could be used as a reliable test in the diagnosis of pulmonary TB when the result is positive. In summary, although ELISA is a simple, rapid, inexpensive method, it is helpful but limited in the diagnosis of pulmonary TB.