HRCT and Whole-Blood Interferon-γ Assay for the Rapid Diagnosis of Smear-Negative Pulmonary Tuberculosis

Abstract

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-γ-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.

Whole Blood Interferon-γ Release Assay Is Insufficient for the Diagnosis of Sputum Smear Negative Pulmonary Tuberculosis

“…If the PTB suspects complained of multiple symptoms, one main complaint from the above list of symptoms was selected by the physician. Among the symptoms of the PTB suspects, the presence of productive sputum, chest pain and weight loss were significantly different between active PTB and non-TB patients, which is comparable to previous studies 8,15,16. Twelve (5.4%) out of 224 suspects complained of weight loss as a main symptom; this complaint was more frequent in active PTB patients among sputum smear negative TB suspects ( p =0.017, McNemar's test) (Table 2).…”

“…Previous studies showed that symptoms such as cough, sputum, fever, hemoptysis, chest pain, and/or weigh loss are meaningful clinical parameters for the diagnosis of sputum smear negative PTB 8,15,16. Therefore, respiratory symptoms such as cough, sputum, hemoptysis, and chest pain, as well as non-respiratory symptoms such as fever and weight loss were investigated through in-person interviews by asking whether symptoms were present or not.…”

“…Several previous studies have evaluated clinical characteristics and scoring systems for the diagnosis of sputum smear negative PTB 8,15,16. Samb, et al8 reported that a chronic cough lasting longer than 3 weeks, chest pains lasting longer than 15 days, the absence of sputum, and the absence of dyspnea are independent predictors of active PTB, but the PPVs of these clinical predictors were only 50%.…”

Characteristics of IFN-γ responses in IGRA among pulmonary TB suspects in a TB-endemic area

“…Generally, the diagnostic value of IGRA alone is disappointing, especially in TB-endemic areas Ling et al, 2011;Metcalfe et al, 2010;Taki-Eddin and Monem, 2012). Combining the results of IGRAs with radiologic features or levels of other cytokines was reported to improve the diagnostic ability of IGRAs (Chiappini et al, 2012;Lee et al, 2010;Wang et al, 2012).…”

There Is More than One Way to Catch a Bug

“…In this issue of Respiration , Lee et al [7] propose another approach for the rapid diagnosis of sputum smearnegative pulmonary TB. In their retrospective analysis of 84 patients with confirmed active pulmonary TB and with a negative sputum smear, they compared the diagnostic value of clinical findings, chest high-resolution (HR) CT, sputum TB-PCR and the IFN-␥ release assay (IGRA) for the diagnosis of active pulmonary TB.…”