of the mtd test reduces inappropriate tuberculosis therapy. the study found the accuracy of the mtd test as follows: overall sensitivity 92% specificity 99% smear positive patients sensitivity 99% specificity 98% smear negative patients sensitivity 62% specificity 99% in 2010 the xpert mtb/rif test, another naat for tb, became commercially available and, as the cdc said in 2015, it began "revolutionizing tuberculosis (tb) control by contributing to the rapid diagnosis of tb disease and drug resistance. the test simultaneously detects mycobacterium tuberculosis complex (mtbc) and resistance to rifampin (rif) in less than 2 hours. in comparison, standard cultures can take 2 to 6 weeks for mtbc to grow and conventional drug resistance tests can add 3 more weeks." the xpert mtb/rif ultra improves upon the xpert mtb/rif test. lam detection assays tests based on the detection of mycobacterial lipoarabinomannan (lam) antigen in urine have emerged as point-of-care tests for tuberculosis (tb). lam antigen is a lipopolysaccharide present in mycobacterial cell walls, which is released from metabolically active or degenerating bacterial cells and appears to be present only in people with active tb disease. urine-based testing have advantages over sputum-based testing because urine is easy to collect and store, and lacks the infection control risks associated with sputum collection. in 2015, who recommended the use of the alere determine tb lam ag assay for people with hiv and a cd4 count below 100 cells/μl and in those defined as seriously ill according to who criteria (respiratory rate >30 breaths per min, body temperature >39 °c, heart rate >120 beats per min, or unable to walk unaided). this recommendation was informed by a cochrane systematic review and meta-analysis of 12 cross-sectional or cohort studies that showed a relatively low pooled sensitivity of 45% and specificity of 92% against a microbiological reference standard. despite the limited sensitivity, test-guided initiation of anti-tb treatment reduced mortality in immunocompromised, hospitalized plhiv. in 2019, an international r&d consortium including find, fujifilm, university of cape town, rutgers university, university of alberta and otsuka funded by ghit completed the development and a first clinical study of the fujifilm silvamp tb point-of-care lam assay. compared with the alere determine tb lam ag assay, the fujifilm silvamp tb lam assay includes novel monoclonal antibodies directed towards the 5-methylthio-d-xylofuranose (mtx) epitope and a silver amplification technology to enable higher diagnostic sensitivity at high specificity. a study with 968 hiv+ hospital inpatients found the fujifilm silvamp tb lam test to have a 28.1% higher sensitivity than the alere determine tb lam ag and the fujifilm silvamp tb lam could diagnose 65% of patients with active tb within 24 h. a meta-analysis with 1,595 inpatients and outpatients showed 70.7% sensitivity and 90.9% specificity for tb diagnosis in people living with hiv for fujifilm silvamp tb lam. the test showed a high positive predictive value (95.2%) in hiv-negative outpatients and has the potential to improve rapid, urine-based tb diagnosis in general populations at the point-of-care. large prospective studies are on the way. interferon-γ release assays interferon-γ (interferon-gamma) release assays (igras) are relatively new tests for tuberculosis. igras are based on the ability of the mycobacterium tuberculosis antigens for early secretory antigen target 6 (esat-6) and culture filtrate protein 10 (cfp-10) to stimulate host production of interferon-gamma. because these antigens are only present in few non-tuberculous mycobacteria or not in any bcg vaccine strain, these tests are thought to be more specific than the tuberculin skin test. the blood tests quantiferon-tb gold in-tube and t-spot.tb use these antigens to detect people with tuberculosis. lymphocytes from the patient's blood are incubated with the antigens. these tests are called interferon γ tests and are not equivalent. if the patient has been exposed to tuberculosis before, t lymphocytes produce interferon γ in response. the quantiferon-tb gold in-tube uses an elisa format to detect the whole blood production of interferon γ. the distinction between the tests is that quantiferon-tb gold quantifies the total amount of interferon γ when whole blood is exposed to the antigens(esat-6, cfp-10 and tb 7.7(p4)), whereas guidelines for the use of the fda approved quantiferon-tb gold were released by the cdc in december 2005. in october 2007, the fda gave approval of quantiferon-tb gold in tube for use in the united states. the enzyme-linked immunospot assay (elispot) is another blood test available in the uk that may replace the skin test for diagnosis. t-spot.tb, a type of elispot assay, counts the number of activated t lymphocytes that secrete interferon γ. for diagnosing latent tb, three systematic reviews of igras concluded the tests noted excellent specificity for the tests to distinguish latent tb from prior vaccination. according to a study from korea, where there is a high prevalence of ltbi, quantiferon-tb gold and t-spot.tb have good sensitivity but reduced specificity for diagnosing active tb, due to their ability to detect latent tb. in a recently published metaanalysis, with data from both developed and developing countries, quantiferon-tb gold in tube had a pooled sensitivity for active tb of 81% and specificity of 99.2%, whereas t-spot.tb had a pooled sensitivity of 87.5% and specificity of 86.3%. in head-to-head comparisons, the sensitivity of igras surpassed tst. however, several subsequent studies have reported higher sensitivity for tst than for igras in patients with active tb; one large study reported a sensitivity of 90% for tst and only of 81% for the quantiferon-tb gold assay. a study at stanford university confirmed that addition of immune boosters can make the igra more reliable in terms of separating positive from negative individuals. a study from the university of southampton shows that variations in environmental temperatures can have a profound effect on the performance of igra. a recently published study from the same group also provided evidence that immunosuppressive agents significantly impair the performance of igras, raising concerns about their reliability in immunosuppressed patients. although, igra replaced the tst in most of the clinical settings but the variability is a concern while reading the result tuberculosis detection using trained rats the international nonprofit organization apopo has been working with sokoine university of agriculture in tanzania to train african giant pouched rats (cricetomys ansorgei) to detect the "scent" of tuberculosis. a recent study shows that "rats increased pediatric tuberculosis detection by 67.6%" and that training these creatures could help address the current challenges related to the diagnosis of this illness in children. tuberculosis classification system used in the us the current clinical classification system for tb (class 0 to 5) is based on the pathogenesis of the disease. the u.s. citizenship and immigration services has an additional tb classification (class a, b1, or b2) for immigrants and refugees developed by the centers for disease control and prevention (cdc). the (class) b notification program is an important screening strategy to identify new arrivals who have a high risk for tb.