Truenat and Line Probe Assay in Pulmonary Tuberculosis: Understanding diagnostic discrepancies at low MTB loads

Anecdotal evidence suggests that a few Tuberculosis patients with Nucleic Acid Amplification Tests (NAAT) result of Low/Very Low are later found to have MTB negative on culture. This study is to assess what proportion of presumptive Pulmonary Tuberculosis (PTB) cases with sputum Truenat showing low or very low MTB levels test positive on Line Probe Assays (LPA) and culture.

This study was conducted among presumptive PTB cases with Truenat showing low or very low MTB levels. Data including LPA and MGIT culture results were retrieved from the NIKSHAY portal, and additional clinical and radiological details were collected.

Among 123 selected cases, 61.8 % were confirmed positive on LPA; 45 cases were culture negative. Discordance was higher in the very low MTB group (45.7 %) compared to the low MTB group (33.0 %). Eleven MGIT culture negative patients with no clinical or radiological features of PTB were not given ATT. None of them had clinical or radiological findings suggestive of PTB on follow-up up to one year.

The discordance of NAAT at low MTB loads with LPA and culture highlights the need for cautious interpretation. The findings underscore the importance of using LPA or MGIT culture for confirmation in suspected PTB cases.