Tuberc Respir Dis (Seoul). 2012 May;72(5):416-25. doi: 10.4046/trd.2012.72.5.416. Epub 2012 May 29.
Factors Associated with Indeterminate and False Negative Results of QuantiFERON-TB Gold In-Tube Test in Active Tuberculosis.
Source
Department of Internal Medicine, Seoul Medical Center, Seoul, Korea.
Abstract
BACKGROUND:
The sensitivities and specificities of interferon-gamma release assays (IGRAs) vary among different population studies, and the data on the routine use of IGRAs are limited. The aim of this study was to evaluate the role of QuantiFERON-TB Gold In-Tube (QFT-GIT) test in the diagnosis of active tuberculosis.
METHODS:
We conducted a prospective study, enrolling 77 patients with suspected pulmonary tuberculosis (TB), at a secondary care teaching hospital in Seoul.
RESULTS:
In total, 12 (15.6%) patients showed indeterminate results due to positive control failure on the QFT-GIT test. Indeterminate results were significantly associated with the elderly, history of the intensive care unit stay, lymphocytopenia, especially low CD4 count, increased C-reactive protein and decreased protein levels. Of the 77 patients, 44 (57.1%) were diagnosed with active pulmonary tuberculosis, and the percentage of false negative results of the QFT-GIT was 36.4% (vs. 31.8% with TST). In the TB group with >65 years old (n=12), the proportions of the indeterminate (33.3% vs. 3.1%) and the false negative results (58.3% vs. 25.0%) of the QFT-GIT were significantly higher than in the younger TB group (n=32).
CONCLUSION:
Indeterminate and false negative results of QFT-GIT test were not infrequent in tuberculosis, especially in the elderly. Care should be considered for the interpretation with the elderly, immunocompromised, chronic and severely diseased patients.
This study appears to be flawed in a number of ways. First, there is no mention of the qualifications of the personnel placing and interpreting the TST, which is notorious for reader innacuracy (in a landmark study (Kendig;CHEST/113/5/May 1998)only 8 of 107 practicing physicians and nurses correctly interpreted one result. The sample size is small (N=77. And the rate of indeterminant results is suspiciously high. In comparision, our state public health laboratory has consistently produced less than a 1% indeterminant results in more than 2000 tests over three years. The unusually high precentage of indeterminiate results may indicate underlying problems with the blood draw, subsequent handling of the specimens, transportation or laboratory processing issues
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