Diagnostic accuracy of TB-LAMP assay on tongue swabs for pulmonary tuberculosis.

Abstract

Tuberculosis (TB) remains a leading cause of infectious disease mortality worldwide. However, underdiagnosis and delayed diagnosis continue to facilitate disease transmission. Tongue swab sampling has emerged as a promising non-invasive alternative for the diagnosis of pulmonary TB. This study evaluated the diagnostic performance of the Eiken TB-LAMP assay when utilizing tongue swab specimens and refined the processing protocols following tongue swab collection. In this prospective study, consecutive outpatients with suspected pulmonary tuberculosis who were able to provide sputum specimens were enrolled. Tongue swab specimens were tested using the WHO-endorsed Eiken TB-LAMP platform (EIKEN CHEMICAL CO., LTD., Tokyo, Japan). Sputum samples were analyzed by Xpert MTB/RIF and culture tests. The microbiological reference standard (MRS) was defined as positivity by either sputum culture or Xpert MTB/RIF. Diagnostic performance was compared to both MRS and Xpert MTB/RIF assay. Among the 243 enrolled participants, 136 (56.0%) were MRS-positive, and 107 (44.0%) were MRS-negative. The tongue swab Eiken TB-LAMP assay achieved a sensitivity of 80.2% (95% CI: 72.5%-86.1%) and a specificity of 94.6% (95% CI: 88.8%-97.5%) compared to sputum Xpert MTB/RIF, and 80.1% sensitivity (95% CI: 72.7%-86.0%) and 98.1% specificity (95% CI: 93.4%-99.7%) compared to the MRS. Sensitivity varied by bacterial load, ranging from 100% (95% CI: 77.2%-100.0%) in high-load cases to 62.5% (95% CI: 45.3%-77.1%) in very-low-load cases. The Eiken TB-LAMP assay using tongue swabs offers a rapid, reliable, and non-invasive diagnostic alternative for TB diagnosis with high specificity and favorable sensitivity. It could significantly reduce the current diagnostic gap, facilitating earlier intervention and helping to curb the ongoing transmission of tuberculosis in high-burden regions.

Importance: Effective control of the disease caused by the bacterium Mycobacterium tuberculosis is often hindered by the challenges of collecting sputum samples and the high costs associated with specialized laboratory equipment. This study examines a new diagnostic approach using tongue swabs combined with loop-mediated isothermal amplification (LAMP). Unlike traditional methods that can be difficult for patients to perform and risky for healthcare workers to manage, tongue swabs are non-invasive, safe, and easy to collect. Because LAMP amplifies DNA under isothermal conditions without requiring thermal cycling, it is more affordable and requires minimal infrastructure, making it particularly suitable for clinics in remote or resource-limited areas. By demonstrating that this approach is effective, the research provides a foundation for faster and more accessible diagnosis. This shift could significantly improve patient care and help bridge the global gap in detecting this infectious disease.