Evaluation of Serological Tests for Immunodiagnosis of Pulmonary Tuberculosis using A60 and Lipoarabinomannan Antigens

Background: Problems in diagnosis of tuberculosis using smear and culture for acid
fast bacilli (AFB) techniques have necessitated the exploration of the utility of
serodiagnosis to support the clinical suspicion of tuberculosis. Three serological
tests, namely Anti-A60 IgG enzyme-linked immunosorbent assay (ELISA), Anti-A60-
IgM (ELISA) using A60 antigen and Mycodot test using lipoarabinomannan (LAM)
antigen were evaluated as tools of diagnosing pulmonary tuberculosis against smear
and culture methods. Materials and Methods: ELISA was used for the detection of
IgG& IgM using A60 antigen, while Mycodot test was performed utilizing
Lipoarabinomannan (LAM) antigen bound to plastic combs in parallel with other
familiar diagnostic methods in 50 patients with pulmonary tuberculosis (Group I),25
patients with chest diseases other than tuberculosis (Group II) and 25 apparently
healthy individuals(Group III) Members of (Group II) & (Group III) participate as
control groups. All members of the three groups were examined for Ziehl-Neelsen
(ZN) smear stains, culture for acid fast bacilli (AFB) and Tuberculin skin test.
Results: ELISA IgG results were positive in 42 (84%) tuberculous patients of Group I
compared to 10 (40%) non tuberculous patients in Group II and 8 (32%) individuals
in Group III. ELISA IgM results were positive in 30 (60%) tuberculous patients of
Group I compared to 3(12%) non-tuberculous patients of Group II and 2 (8%)
individuals of Group III. Mycodot test results were positive in 33 (66%) tuberculous
patients in Group I compared to 6 (24%) non-tuberculous patients in Group II and 3
(12%) individuals of Group III. The overall sensitivities and specificities of the three
tests (Mycodot, IgG and IgM) were obtained on basis of the receiver operating
characteristic (ROC) curve for each test and comparison of (ROC) curves of the
three tests and they were (66 , 82%) for Mycodot test, (80 , 92%) for Anti-A60 IgG
and (82,74%) for Anti-A60 IgM. Positive predictive values and negative predictive
values were (78.57, 70.69%) for Mycodot test, (90.91, 82.14%) for IgG and (75.93,
80.43%) for IgM. Results of Ziehl-Neelsen (ZN) smear stains and culture for Acid fast
Bacilli (AFB) were positive in all members of group (I), while were negative in all
members of control groups { group (II) and group (III) }. Tuberculin skin tests were
positive in 46(92%) tuberculous patients of group (I), 7 of 20 (35%) non-tuberculous
patients and 3 of 15 (20%) individuals of group III. Conclusion: Anti A60 IgG ELISA
was the best serodiagnostic technique compared with Anti 60 IgM ELISA and  Mycodot test. The high diagnostic performance of Anti 60 IgG makes it a useful, Simple and rapid supporting tool to confirm the clinical judgment of tuberculosis when used as an adjunct to symptoms and signs together with other investigation tools.