HRCT and whole-blood interferon-gamma assay for the rapid diagnosis of smear-negative pulmonary tuberculosis.

BACKGROUND Early diagnosis of active pulmonary tuberculosis (PTB) is critical for TB control, and difficult in patients with smear-negative sputum. OBJECTIVE We wanted to evaluate the usefulness of clinical findings, high-resolution computed tomography (HRCT), interferon-gamma-releasing assay (IGRA) and polymerase chain reaction (PCR) of sputum in the diagnosis of smear-negative PTB. METHODS From June 2006 to September 2008, 178 patients with suspected PTB on the basis of clinical and radiological findings visited our institute. After excluding smear-positive cases (n = 77) and cases with an inconclusive diagnosis (n = 17), we studied 84 patients. Their clinical records, HRCT, sputum TB-PCR assay and IGRA results were retrospectively evaluated. A QuantiFeron-TB Gold (QFT-G; Cellestis Ltd., Carnegie, Vic., Australia) assay was used for the IGRA. RESULTS Active PTB was diagnosed in 40 (48%) of 84 patients; lack of sputum and young age were significantly associated with an increased risk of PTB. The sensitivities of sputum PCR assay, IGRA, and HRCT were 43.2, 84.4 and 80.0%, respectively, and the specificities were 97.7, 82.9 and 70.5%, respectively. Among the 38 patients suspected of having PTB based on HRCT, 24 patients showed positive results on the IGRA, and 23 of these were diagnosed with active PTB. Among the 35 patients suggested not to have TB based on HRCT, 25 showed negative results on the IGRA, and 23 (92%) of these were diagnosed as not to have TB. CONCLUSION The combined results of HRCT and the IGRA could help decision-making for early initiation of treatment in smear-negative patients.