Evaluation of the PATHFAST TB LAM Ag assay as a treatment monitoring tool for pulmonary tuberculosis in Nairobi, Kenya.

Background: Treatment monitoring is important in pulmonary tuberculosis (PTB) management, since prolonged treatment necessitates regular assessments to prevent treatment failure and the emergence of drug-resistant strains. However, the lack of a simple, rapid, and reliable treatment monitoring tool (TMT) remains a major challenge. We evaluated the utility of measuring sputum lipoarabinomannan (LAM) concentration by the PATHFAST TB LAM Ag assay (PHC Corporation, Tokyo, Japan) as a TMT in patients with PTB in Nairobi, Kenya.

Methods: We retrospectively analyzed sputum LAM levels via the PATHFAST TB LAM Ag assay from a Nairobi cohort of patients with PTB and compared these results with conventional microbiological tests (acid-fast bacilli [AFB] smear microscopy; mycobacterial growth indicator tube [MGIT] culture). Stored sputum pellets processed with N-acetyl-L-cysteine (NALC)-NaOH were used for LAM measurement. Serial LAM concentrations measured every 2 weeks over an 8-week period were compared across bacterial load categories to assess correlations with AFB smear grades and culture results using the Kruskal-Wallis and Mann-Whitney U tests.

Results: The 98 patients included here had a median age of 37 years (Interquartile Range: 27-44). The majority were men (74/98, 75.5%) and the MGIT culture was positive for 89 (90.8%) of them. Patients with elevated baseline LAM concentrations showed a significant reduction in LAM levels with treatment (90% median reduction by week 8), whereas those with low baseline LAM concentrations did not show a declining trend. Sputum LAM levels were significantly higher in culture-positive samples compared to culture-negative samples (23.8 pg/mL vs. 10.8 pg/mL, P < 0.001). Sputum LAM levels showed a significant correlation with AFB smear grades, with median concentrations increasing progressively from 11.3 pg/mL in smear-negative samples to 19.7 pg/mL in scanty/1 + samples, and 46.7 pg/mL in 2 + /3 + samples (P = 0.0001). LAM levels were significantly higher in culture-positive/AFB-positive sputum samples (viable bacilli) than in culture-negative/AFB-positive samples (non-viable bacilli) (P < 0.0001).

Conclusion: Our findings revealed that sputum LAM concentration declined during TB treatment, particularly among patients with high baseline levels, and correlated with AFB smear grades and culture results. Additionally, LAM concentrations differed between culture-positive and culture-negative samples among AFB smear-positive samples. Further prospective studies are needed to assess LAM levels as a TMT.