Assessment of Quanti FERON-TB Gold (In-Tube) Test in Tuberculosis Diagnosis

Because of uncertainty in interpretation of some tests for diagnosing TB, decision making for the tuberculosis treatment is based on multiple diagnostic tests. This study was conducted to assess the accuracy of Quanti FERON-TB Gold test in tuberculosis diagnosis.

The study was carried out on 30 cases and 46 controls. Statistical indices of sensitivity, specificity, positive predictive value, negative predictive value, likelihood ratios, odds ratio and Receiver Operating Characteristics (ROC) curve were estimated.

Sensitivity of QFT-G was 90.0% (95% CI=73.0-97.6), specificity 95.7% (95% CI=83.8-99.3), positive predictive value 93.1% (95% CI=76.3-98.9), negative predictive value 93.6% (95% CI=81.3-98.4). The area under ROC curve was 0.942 (95% CI=0.88-1.00), that significantly differed from chance diagonal area (P<0.0001). The optimum cut point for the Quanti FERON-TB Gold test was 0.35 IU/ml, with sensitivity of 0.90 and specificity of 0.957.

The Quanti FERON-TB Gold test displayed good validity indices in this study. Since the utility of this test has a high cost therefore this test would not be offered for routine tuberculosis detection. It suggested that this test are applicable for smear and culture negative tuberculosis, child tuberculosis, and assessment of TB contact tracing.