Influencial factors of the performance of interferon-γ release assays in the diagnosis of childhood tuberculosis

Diagnosis of active tuberculosis (TB) in children remains difficult. This study aimed at evaluating the ability of interferon-gamma release assays (IGRAs) in the detection of active TB in human immunodeficiency virus-negative children vaccinated with Bacille Calmette–Guérin and investigating the effect of prednisolone treatment on the IGRAs performance. Among the 162 children with suspected TB disease recruited in China, 60 were tested with QuantiFERON-TB Gold In Tube (QFT-GIT) and 102 were tested with T-SPOT.TB. QFT-GIT presented a sensitivity of 83.9 % (95 % CI 66.9–93.4 %) and a specificity of 88.5 % (95 % CI 70.2–96.8 %), while T-SPOT.TB had a sensitivity of 75.9 % (95 % CI 63.4–85.2 %) and a specificity of 94.7 % (95 % CI 81.8–99.5 %). The positive predictive value was high in both assays, 92.9 % for QFT-GIT and 95.7 % for T-SPOT.TB. In total of these two kinds of IGRAs, false negative rate was significantly higher in children receiving systemic prednisolone (1 mg/kg/day) therapy for >1 week (two tested with T-SPOT.TB and five tested with QFT-GIT) than in those with ≤1 week of prednisolone therapy and without prednisolone therapy (57.1 vs. 18.3 %, p = 0.035). There was no significant difference of the positive rate of both tests in children <5 years old compared with those ≥5 years old. Both types of IGRAs showed good diagnostic values in detecting childhood TB before microbiological evidence was available. Glucocorticoids had a significant negative influence on IGRAs if treated for >1 week. Age made no difference on the performance of these tests in children.