PURPOSE: Immunocompromised patients are one of the most important targets for screening of latent TB infection (LTBI0. Rapid diagnosis of active pulmonary TB (PTB) infection especially in setting of negative sputum smear for AFB is an important goal of TB control programs. QuantiFERRON TB gold In Tube(QFT-IT) has been shown to improve diagnostic accuracy for diagnosing LTBI. The present study investigated the performance QFT-IT assay for the diagnosis of LTBI and active PTB infection in both immuno-compromised and in immuno-competent patients.
METHODS: We conducted a retrospective study on 100 patients (50 immuno-compromised and 50 immuno-competent). All patients were suspects of PTB infection based on clinical and radiological findings. All patients had sputum smear negative for AFB and underwent tuberculin skin test (TST), CXR, sputum smear and culture for AFB, and QFT-IT.
RESULTS: Both TST and QFT-IT tests had significantly lower percentage of positive results in immuno-compromised compared to immuno-competent patients (10% vs. 60% for TST and 26% versus 66% for QFT-IT; p 0.001).QFT-IT test had a significantly higher percentage of positive result in both immuno-compromised and immuno-competent patients when compared to TST. Indeterminate QFT-IT results were more significantly high in immuno-compromised than immuno-competent patients (10% vs. 4%, p 0.001). QFT-IT had a higher sensitivity and negative predictive value when compared to TST in diagnosis of both latent and active TB infection.
CONCLUSION: QFT-IT has highly sensitive test but has low specificity for detection of both latent and active TB infection. Poor specificity of QFT-IT test is attributed to the high prevalence of LTBI in our setting. QFT-IT test is very useful test compared to TST especially in immunocompromised patient with LTBI. Negative QFT-IT test results should be interpreted in conjunction with clinical, radiological and bacteriological diagnostic finding.
CLINICAL IMPLICATIONS: QFT-IT test is highly sensitive test in diagnosis of both latent and active PTB infection. QFT-IT should be used in conjunction with clinical, radiological and bacteriological diagnostic tests for diagnosis of active pulmonary TB infection.
DISCLOSURE: Nadia Hasaneen, No Financial Disclosure Information; No Product/Research Disclosure Information