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

¹ Division of Respiratory Diseases, Dept of Medicine, Kawasaki Medical School, 577 Matsushima, Kurashiki, Japan

^* To whom correspondence should be addressed. E-mail: yoshihiro{at}med.kawasaki-m.ac.jp.

	Abstract

We assessed risk factors that can promote indeterminate results of QuantiFERON TB-2G (QFT-2G) tests.

The subjects were 704 patients suspected of tuberculosis (TB) and latent tuberculosis infection (LTBI) between January 2005 and December 2007. The QFT-2G test and tuberculin skin test (TST) were performed for all subjects. If the results of QFT-2G test were indeterminate, this test was repeated within one month.

Among 704 patients, 72 patients (10.2%) showed indeterminate results on QFT-2G test. Indeterminate results were due to positive control failure in 68 patients (88.9%) and negative control failure in four. Although the results of TST were negative for 64 patients showing indeterminate results, the remaining eight patients showed a positive response on TST. Indeterminate results were significantly associated with elderly and immunocompromised patients. Lymphocytopenia and hypoalbuminemia were significantly associated with indeterminate laboratory findings. When QFT-2G test was repeated for all patients showing indeterminate results, 12 patients (16.7%) demonstrated determinate results on the subsequent test.

Indeterminate results of QFT-2G test under routine clinical practice are not infrequent. When scoring QFT-2G test results for elderly and immunocompromised patients, one must be careful because the possibility of obtaining determinate results may be low even if this test is repeated.