Diagnosis of tuberculosis by a visually detectable immunoassay for lipoarabinomannan

Recovery of tubercle bacilli from sputum, tissue, or body fluid is the stan dard for the diagnosis of tuberculosis (TB) although this process is techni cally demanding and relatively insensitive. We have developed a simplified, visually detectable, colloidal gold-based serological assay to qualitative ly detect IgG directed against the mycobacterial cell wall component lipoar abinomannan (LAM). The objective of this investigation is to determine the accuracy of this assay in patients with active pulmonary TB and in control patients with or without latent infection. In patients with active TB, the sensitivity of anti-LAM IgG was 85 to 93%. In five patients with active TB who were smear-negative, all tested positive for anti-LAM IgG. The specific ity of the test depended on the presence of tuberculous infection. In U.S, citizens comprised of young healthy adults and rheumatology patients, the s pecificity was 100%. In an at-risk population for tuberculous infection who were either tuberculin skin test-negative or positive, the specificity was 89%. The negative and positive predictive values of the test were 98% and 52% respectively. We conclude that anti-LAM IgG immunoassay is relatively s ensitive and specific for active TB and thus, a potentially useful screenin g test for active TB.