Advances in Diagnostics of Pulmonary TB: What Is the Latest Approach to Diagnose Pulmonary TB?

Abstract

The gold standard for diagnosing pulmonary TB is to detect Mycobacterium tuberculosis (M. TB) in a human specimen. Case detection methods vary depending on the medical resources and economic conditions in each region. These methods can be either passive, in which case the disease is diagnosed after the patient has had a consultation, or active, when infections are detected via screening and medical examination. In countries with low TB prevalence, passive case detection is the primary method used, and clinicians deal with many other diseases as well, so various tests have been developed to diagnose pulmonary TB and other diseases. Passive case detection is used in areas where TB is widespread and in populations in which infections are particularly common, especially when medical resources, efficient diagnostic methods, and commonly used tests are limited in the area. Thus, the choice of diagnostic method used depends strongly on the local situation. The number of TB patients worldwide is gradually declining in most countries. To accelerate the decline in infections, the World Health Organization (WHO) has devised various measures for bacterial testing in the focal region. In 2021, the WHO once again recommended rapid and accurate sputum testing to increase the number of patients for whom treatment is initiated and to accelerate and improve the efficiency of TB diagnosis. This is being done with the aim of reducing the number of patients, deaths, and cases with multidrug-resistant TB not just drug-sensitive TB. The WHO has recommended converting from the conventional smear method to the nucleic acid amplification test (NAAT). As culture tests are expensive, it is recommended that patients be triaged first via symptomatic screening and digital imaging tests to reduce the number of target patients, after which the NAAT should be performed. For this triage process, testing methods using human specimens that can be obtained more easily are under development. There are many benefits to early detection of pulmonary TB and rifampicin (RFP)-resistant cases. However, in countries where the prevalence of TB has declined, the diagnosis of other diseases is also important, so approaches such as bronchoscopy and positron emission tomography (PET) are used for patients who cannot be diagnosed using the NAAT. The onset of TB in people living with HIV (PLWHIV) has become a major problem of this coinfection, regardless of the local prevalence of TB. Lipoarabinomannan has been developed as a biomarker for this population, and since it uses an easily available sample (urine), it is used both in the triage process and in the low-prevalence areas. Many diagnostic methods will be developed in the future, but the latest approach to diagnosing TB is to suspect it and then perform a NAAT.