Factors influencing discordant results of the QuantiFERON-TB Gold In-tube test in patients with active TB.

OBJECTIVES

Indeterminate or negative results from the QuantiFERON-TB Gold In-tube test (QFT-GIT) for TB-confirmed patients indicate the lower sensitivity of this method. The aim of this study was to determine the factors associated with indeterminate and negative QFT-GIT results in active TB patients.

METHODS

We analyzed retrospectively the laboratory and clinical data of patients diagnosed with TB between December 2009 and April 2012 at a tertiary university hospital in Seoul, Korea.

RESULTS

Among 1301 patients who underwent QFT-GIT, TB-PCR and TB-culture, 168 (12.9%), those with positive TB-PCR or TB-culture were diagnosed with TB. Thirty-nine (23.2%) had indeterminate or negative results by QFT-GIT assay, which did not correlate with positive results of TB-PCR or TB-culture. These patients were older, had lower lymphocyte, total protein and albumin levels, and showed significantly higher CRP levels than the positive group. Multivariate logistic regression analysis showed that the probability of indeterminate and negative QFT-GIT results increased as CRP (odd ratio, 1.069; 95% CI, 1.013-1.127; P = 0.014) or age (1.030, 1.005-1.056, 0.02) increases.

CONCLUSIONS

When levels of markers of inflammation, such as CRP, are high or the patient is older, QFT-GIT results should be interpreted carefully and correlated with additional tests for TB.