Background: The high positive responses obtained in active TB indicate that IGRAs may be useful in diagnosing active TB. This study aimed at evaluating the usefulness of Quantifer on-TB Gold-in Tube test (QFT-IT) in the diagnosis of active TB among Nigerians.
Methods: This study prospectively enrolled sputum smear positive TB cases and healthy disease free controls. Basic demographic and clinical data were collected using a structured questionnaire. Venous blood was collected into the QTF-IT tubes, incubated for 16-24 hours, serum harvested and stored at -200C till analysed in a batch. Tuberculin skin test (TST) was also done using 5TU and read within 48-72 hours. The performances of QFT-IT and TST among the cases and controls were compared.
Results: Sixty one TB cases and 41 controls were enrolled. The mean (SD) age of the TB cases was higher than the controls, 35.14+4.3 yrs v 27.8 + 2.1, p<0.001. Forty three (70.5%), 13 (21.3%) and 5 (8.2%) of the cases had a positive, negative and indeterminate QFT-IT results respectively compared with 14 (34.1%), 25 (61%), and 2 (4.9%) of the controls respectively, p values <0.001, 0.005 and 0.05 respectively. Fifty eight(95%) and 29(70.7%) of the TB cases and controls had a positive TST result respectively while 3 (5%) and 12( 29.3%) of the TB cases and controls had a negative TST result respectively, p values 0.003 each .QFT-IT had a sensitivity of 76% (95% CI 61.8 -85.2%) while the sensitivity of TST was 96.6% (95% CI 88.5 -98.3%), p = 0.07. The specificity of QFT-IT was 63.7% (95% CI 46-76%) and 30% (95% CI 20- 56%) for TST, p =0.001. Positive Likelihood ratio was 1.7 (95% CI 1.06-2.85) for QFT-IT and 1.4 (95%CI 1.06-1.8) for TST, p =0.002. Among the cases, both TST and QFT-IT were positive in 43(70.5%) and both negative in 1 (1.6%), and overall test .agreement was 77.7% (Kappa =0.13; p= 0.07). Female sex and higher total lymphocytes count were significantly associated with a positive QFT results.
Conclusion: IGRA has a higher specificity and positive likelihood ratio in TB cases. Our findings indicate that QFT-IT may be a good adjunct tool to diagnose TB disease.