Comparative study between using QuantiFERON and tuberculin skin test in diagnosis of Mycobacterium tuberculosis infection

Aim: Study degree of sensitivity and specificity of IFN-γ as QuantiFERON-TB Gold In-Tube assay in diagnosis of tuberculosis instead of tuberculin test.Subjects and methods: Forty patients were included in this study subdivided into two groups. First included 20 patients with sputum positive for tuberculosis, while the second included 20 patients suspected to catch TB infection, guided by: clinical and radiological examinations with smear negative for TB. Control group included 10 clinical and radiological healthy controls previously vaccinated by BCG with positive tuberculin test. All subjects were submitted for full clinical history physical examination routine laboratory tests, plain chest X-ray, sputum study for acid fast Bacilli by Ziehl–Neelsen stain, tuberculin test using Mantoux technique, sputum culture on Lowenstein-Jensen Medium and QuantiFERON-TB Gold In-Tube (QFT-Gold IT) assay.Results: QFT-Gold IT test sensitivity = 100% specificity = 100% predictive value positive = 100% which means that 100% of the disease positive patients gave positive QFT-Gold IT test and predictive value negative = 100% which means that 100% of the disease negative patients gave negative QFT-Gold IT test. Agreement between tuberculin test and QFT-Gold IT test was good agreement where the ‘κ’ was 0.65 (CI = 0.39–0.91). Study revealed positive correlation between QuantiFERON level and severity of infection in sputum, which was statistically significant, where ‘r’ was 0.92 and P-value was <0.05.Conclusion: QFT-Gold IT, has excellent sensitivity and specificity unaffected by BCG vaccination. Tuberculin test specificity is high in non-BCG-vaccinated populations but low and variable in BCG vaccinated populations