Pragmatic accuracy of an in-house loop-mediated isothermal amplification (LAMP) for diagnosis of pulmonary tuberculosis in a Thai community hospital

Abstract

Background To improve the quality of diagnosing pulmonary tuberculosis (TB), WHO recommends the use of rapid molecular testing as an alternative to conventional microscopic methods. Loopmediated isothermal amplification assay (LAMP test) is a practical and cost-effective nucleic amplification technique. We evaluated the pragmatic accuracy of an in-house LAMP assay for the diagnosis of TB in a remote health care setting where an advanced rapid molecular test is not available. Methods A prospective diagnostic accuracy study was conducted. Patients with clinical symptoms suggestive of TB were consecutively enrolled from April to August 2016. Sputum samples were collected from each patient and were sent for microscopic examination (both acid-fast stain and fluorescence stain), in-house LAMP test, and TB culture. Results One hundred and seven patients with TB symptoms were used in the final analysis. This included 50 (46.7%) culture-positive TB patients and 57 (53.3%) culture-negative patients. The overall sensitivity of the in-house LAMP based on culture positivity was 88.8% (95/107) with a 95%CI of 81.2-94.1. The sensitivity was 90.9% (40/44) with a 95%CI of 78.3-97.5 for smear-positive, culture-positive patients, and was 16.7% (1/6) with a 95%CI of 0.4-64.1 for smear-negative, culture-positive patients. The overall sensitivity of the in-house LAMP test compared to smear microscopy methods were not significantly different (p = 0.375). The

Performance of Loop-Mediated Isothermal Amplification (LAMP)-Lateral Flow Detection and Xpert MTB/RIF Ultra for Diagnosis of Pulmonary Tuberculosis

“…Moreover, this study found that sputum C/S for TB could produce only 57% of M. tuberculosis, resulting in lower specificity of LAMP-LFD assay and Xpert MTB/RIF ultra than other studies. This finding conformed to that of Toonkomdang et al [10], who found that only 47% of positive TB cultures. This implied that without molecular test, diagnostic errors could occur.…”

“…The results in this study agreed with those of Pham et al [9] who found that TB-LAMP had better performance in diagnosing TB in the positive smear group (97.9% sensitivity)than in the negative smear group (46.6% sensitivity). In Thailand, Toonkomdang et al [10] found that the performance of in-house LAMP assay in the positive smear group (sensitivity 90.9%) was higher than that in the negative smear group (sensitivity 16.7%).…”

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“…There are several additional diagnostic methods for diagnosing TB, like the loop-mediated isothermal amplification (LAMP), which utilises the isothermal amplification procedure. This method is recognised by the WHO, though it's use is hampered by the poor sensitivity among the sputum negative samples and the prohibitive costs of the reagents used (Gelaw et al, 2017;Toonkomdang et al, 2020). The line probe assay (LPA), is yet another test that uses PCR to amplify DNA from Mtb and the output is applied to immobilised oligonucleotides on a strip which emits a colorimetric signal, signifying the presence of drug sensitive and drug resistant strains to isoniazid and rifampicin by the presence of gene mutations within the sample.…”

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“…Additionally, in the case of lowresource settings, the amplification can be monitored by using a cheap turbid meter and, after, the addition of an intercalating agent [126]. LAMP has been used previously as a tool to diagnose diseases such as malaria [122] and tuberculosis [127].…”