SUMMARY AND EXPLANATION THE TEST
Tuberculosis is a chronic, communicable disease caused principally by M. TB hominis (Koch’s bacillus), occasionally by M. TB bovis. The lungs are the primary target, but any organ may be infected.
The risk of TB infection has exponentially declined in the 20th century. However, the recent emergence of drug-resistant strains1, particularly among patients with AIDS2, has rekindled interest in TB. The incidence of infection was reported around 8 million cases per year with a death rate of 3 million per year. The mortality exceeded 50% in some African countries with high HIV rates.
The initial clinical suspicion and radiographic findings, with subsequent laboratory confirmation by sputum examination and culture are the traditional method(s) in the diagnosis of active TB5,6. However, these methods either lack sensitivity or are time consuming, in particularly are not suitable for patients who are unable to produce adequate sputum, smear-negative, or suspected to have extra-pulmonary TB.
The TB IgG/IgM Combo Rapid Test is developed to alleviate these obstacles. The test detects IgM and IgG anti-M.TB in serum, plasm, or whole blood in 15 minutes . An IgM positive result indicates for a fresh M.TB infection, while an IgG positive response suggests a previous or chronic infection. Utilizing M.TB specific antigens, it also detects IgM anti-M.TB in patients vaccinated with BCG. In addition, the test can be
performed by untrained or minimal skilled personnel without cumbersome laboratory equipment.
PRINCIPLE
The TB IgG/IgM Rapid Test is a lateral flow chromatographic immunoassay. The test cassette consists of: 1) a burgundy colored conjugate pad containing M.TB antigens conjugated with colloid gold (M.TB conjugates) and rabbit IgG-gold conjugates, 2) a nitrocellulose membrane strip containing two test bands (M and G bands) and a control band (C band). The M band is pre-coated with monoclonal anti-human IgM for the detection of IgM anti- M.TB, the G band is pre-coated with reagents for the detection of IgG anti-M.TB, and the C band is pre-coated with goat anti-rabbit IgG.
When an adequate volume of test specimen is dispensed into the sample well of the cassette, the specimen migrates by capillary action across the cassette. IgM anti-M.TB if present in the specimen will bind to the M.TB conjugates. The immunocomplex is then captured on the membrane by the pre-coated anti-human IgM antibody, forming a burgundy colored M band, indicating a M.TB IgM positive test result. IgG anti- M.TB, if present in the specimen, will bind to the M.TB conjugates. The immunocomplex is then captured by the pre-coated reagents on the membrane, forming a burgundy colored G band, indicating a M.TB IgG positive test result. Absence of any test bands (M and G) suggests a negative result. The test contains an internal control (C band) which should exhibit a burgundy colored band of the immunocomplex of goat anti rabbit IgG/rabbit IgG-gold conjugate regardless of the color development on any of the T bands. Otherwise, the test result is invalid and the specimen must be retested with another device.
