Clinical evaluation of the diagnostic performances and treatment monitoring of the new PATHFAST TB LAM Ag assay in sputum specimens of patients with tuberculosis or with nontuberculous mycobacteria pulmonary disease

ABSTRACT Diagnosing pulmonary tuberculosis (TB) and monitoring treatment remain challenging. New tools such as the PATHFAST TB LAM assay (PHC Corporation, formerly LSI Medience Corporation, Tokyo, Japan; distributed by BioSynex, France; PF-LAM) may complement microscopy, culture, and NAAT. PF-LAM is an immunoassay quantifying lipoarabinomannan (LAM), a mycobacterial cell wall component, in sputum within 1 hour using an automated chemiluminescent reader. Diagnostic performance was first assessed on 100 sputum samples: 40 culture-positive for Mycobacterium tuberculosis complex (MTBC), 40 culture-positive for nontuberculous mycobacteria (NTM), and 20 culture-negative for both. We then tested 61 longitudinal sputum samples from 19 pulmonary TB patients under treatment. Four additional samples from one patient with NTM pulmonary disease (NTM-PD) were also tested. PF-LAM showed 75% sensitivity for MTBC detection, with a strong correlation between LAM concentration and culture time-to-positivity (Spearman ρ = 0.915, P < 0.0001). Specificity was 95% on culture-negative specimens. The test was also positive for 26/40 (65%) NTM-culture-positive samples. Notably, 19 of these 26 samples were obtained from NTM-PD patients, yielding 73% sensitivity for NTM-PD detection. The assay’s potential for treatment monitoring was demonstrated by significant negative correlations between LAM concentration and (a) treatment duration (ρ=–0.434, P = 0.0012) and (b) time to positive culture (ρ=–0.665, P < 0.0001). PF-LAM is a rapid and easy-to-use test for diagnosing pulmonary TB. While NTM cross-reactivity reduces specificity, it may provide diagnostic value for NTM-PD. Results on monitoring TB treatment are promising as no test is currently available for this indication. IMPORTANCE Effective monitoring of the treatment response is essential for successful tuberculosis (TB) management as prolonged therapies require accurate evaluation to prevent relapse, treatment failure, or drug resistance. This study highlights the diagnostic and treatment-monitoring potential of the PATHFAST TB LAM Ag assay, which quantifies lipoarabinomannan (LAM) concentrations in sputum samples and correlates with bacterial load. For the first time, we also demonstrate the assay’s applicability for detecting and monitoring nontuberculous mycobacterial (NTM) pulmonary diseases, which are increasingly prevalent in industrialized countries. The semi-automated, rapid format (<17 minutes) of the PATHFAST TB LAM Ag assay provides a simple and reliable approach for assessing bacillary load during treatment, representing a promising tool for improving patient management and diagnostic efficiency in both TB and NTM-PD.