Indeterminate results of QuantiFERON TB-2G test performed in routine clinical practice

The present authors assessed risk factors that can promote indeterminate results of QuantiFERON TB-2G (QFT-2G; Cellestis Ltd, Carnegie, Australia) tests. The subjects were 704 patients with suspected tuberculosis (TB) and latent TB infection between January 2005 and December 2007. The QFT-2G test and the tuberculin skin test (TST) were performed for all subjects. If the results of the QFT-2G test were indeterminate, the test was repeated within 1 month. In total, 72 (10.2%) patients showed indeterminate results on the QFT-2G test. Indeterminate results were due to positive control failure in 68 (88.9%) patients and negative control failure in four patients. The results of the TST were negative for 64 patients showing indeterminate results, the remaining eight patients showed a positive response to the TST. Indeterminate results were significantly associated with elderly and immunocompromised patients. Lymphocytopaenia and hypoalbuminaemia were significantly associated with indeterminate laboratory findings. When the QFT-2G test was repeated for all patients showing indeterminate results, 12 (16.7%) patients demonstrated determinate results on the subsequent test. Indeterminate results of the QuantiFERON TB-2G test under routine clinical practice are not infrequent. When scoring QuantiFERON TB-2G test results for elderly and immunocompromised patients, one must be careful because the possibility of obtaining determinate results may be low even if the test is repeated.