Evaluation of QuantiFERON microtube, using 0.9 mL blood, for diagnosing tuberculosis infection

The performance of QuantiFERON microtube (QFT-MT), using 0.9 mL blood, and QuantiFERON-TB Gold in-tube test (QFT-IT) (3 mL blood), for diagnosing tuberculosis (TB) was compared in children and adults in an endemic setting. In 152 children with suspected TB and 87 adults with confirmed TB, QFT-IT was compared with two QFT-MT concentrations (QFT-MT A and B). Proportions of positive and indeterminate results, interferon (IFN)-γ responses, interassay agreement and sensitivity were assessed. We found similar proportions of indeterminate results, levels of IFN-γ and comparable sensitivity. The interassay agreement was moderate in all children (QFT-IT versus QFT-MT A: 85%, k=0.44 and QFT-IT versus QFT-MT B: 88%, k=0.50) and adults (QFT-IT versus QFT-MT A: 88%, k=0.50 and QFT-IT versus QFT-MT B: 89%, k=0.49). Sensitivity was low (QFT-IT 23%, QFT-MT A 18% and B 19%) in children with confirmed or highly probable TB compared with adults (83%, 86% and 88%, respectively). The QFT-MT test can be reliably performed using less than one-third of the blood volume used in QFT-IT. The reduced volume may be useful for research and future diagnosis of paediatric TB. The poor sensitivity and high indeterminate rate of both IFN-γ release assays in severely ill children, with immature or impaired immunity in an endemic setting, warrants further investigations.