Rapid liposomal agglutination card test for the detection of antigens in patients with active tuberculosis

SETTING: A total of 1360 subjects with clinically confirmed pulmonary and extra-pulmonary tuberculosis (TB) and other non-tuberculous conditions. OBJECTIVES: To develop a rapid, sensitive and specific diagnostic test for the detection of the glycolipid antigen of Mycobacterium tuberculosis in a variety of clinical samples. STUDY DESIGN: Affinity-purified rabbit anti-glycolipid antibodies (IgG) were coupled to liposome particles (0.2-0.4 mu m) in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinamide to prepare the working reagent of the TB/M card test. RESULTS: Antibody-conjugated liposomes, when determined with the glycolipid antigens present in the specimens, formed a dark blue agglutination within 4 min. No clumping was observed in samples from normal healthy subjects or patients with other diseases. The test was shown to be effective in detecting glycolipid antigens of M. tuberculosis in clinical samples from patients with active TB with as low as 1 ng/ml analytical sensitivity, 97.4% clinical sensitivity and 96.9% specificity. CONCLUSION: The TB/M card test was found to be comparatively economical (4 Indian Rupees or US$ 0.09/test), rapid (4 min) and seems fairly useful for mass testing of a variety of biological specimens (cerebrospinal, pleural and synovial fluids, serum, tissue biopsy extract) from patients with tuberculous meningitis, pulmonary TB and other extra-pulmonary TB in endemic countries.