Clinical relevance of false-negative interferon-gamma release assays in patients with tuberculous pleurisy in an intermediate tuberculosis burden country

Background: There have been few studies to verify factors associated with a false-negative interferon-gamma release assay (IGRA) in patients with tuberculous pleurisy. We investigated the clinical relevance of false-negative results of the blood QuantiFERON-TB Gold In-Tube (QFT-GIT) assay and its risk factors in patients diagnosed with pleural tuberculosis (TB). Methods: Medical records of 650 pleural TB patients in a tertiary hospital between January 2009 and December 2020 were reviewed retrospectively. Patients who underwent the blood QFT-GIT assay and pleural fluid analysis before starting anti-TB medication were included. Results: Of 199 patients with pleural TB who were performed QFT-GIT assay, 36 (18.1%) were false-negative results. These patients tended to be older than those with a positive result (P=0.060). The QFT-GIT-false-negative group of had significantly more comorbidities such as end-stage renal disease (ESRD), haematological cancer or pneumoconiosis than the QFT-GIT-positive group. Hypoproteinaemia and pH >6 in pleural fluid were associated with a false-negative QFT-GIT. Of the 199 patients, 163 (81.9%) were cured or completed anti-TB treatment; 13 patients (6.5%) died. The QFT-GIT-negative patients had significantly worse outcomes including mortality [unfavourable outcome: 33.3% (12/36 patients) in QFT-GIT-negative groups vs. 14.7% (24/163 patients) in QFT-GIT-positive groups, P<0.017; overall mortality: 16.7% (6/36 patients) vs. 4.3% (7/163 patients), respectively, P<0.015]. Conclusions: In pleural TB, a false-negative QFT-GIT result was 18.1% in a country of intermediate TB incidence. This discordant result in GFT-GIT was associated with ESRD, pneumoconiosis, hypoproteinaemia and a poor outcome. Clinicians should keep in mind the possibility of false-negativity in the blood IGRA test, especially in specific situations and its impact on TB outcome in managing patients with pleural TB.