Tuberk Toraks 2016;64(2):182-183
Ülkemizden quantiferon Tb gold in tube indeterminant sonuçlari
Yeşim GÜROL1, Gülden ÇELİK1
1 Yeditepe Üniversitesi Tıp Fakültesi, Tıbbi Mikrobiyoloji Anabilim Dalı, İstanbul, Türkiye
1 Department of Medical Microbiology, Faculty of Medicine, Yeditepe University, Istanbul, Turkey
Interferon gamma release assays (IGRAs) are used worldwide alternative to tuberculin skin test (TST). The sensitivity and specificity of these tests are 78-90%, 93-99%. There are some limitations of IGRAs such as indeterminate results. As we use Quantiferon TB Gold in Tube (QFT-2G) in our laboratory, we have also found some indeterminate results especially in some age groups. The aim of our study was to share the rate of indeterminate results from our country comparing to other studies worldwide.
We evaluated the results of QFT-2G tests during six year period (2006-2012) and we detected 1625 negative, 559 positive and 93 indeterminate test results among 2277 patients. The test was performed as the manufacturer's instructions. The rate of indeterminate result was 4%. The distribution of the indeterminate results according to the age groups were as follows; 30 in 1-10 ages (30.2%), 12 in 61-70 ages (13.04%) (Table 1).
There are few studies about the relationship between interferon gamma production and age. In a study of a large pediatric population, indeterminate results were found more frequent with QFT-IT than the other IGRA (T SPOT TB) especially in children < 4 years of age as 12.6% vs 2.3% (1). Although the indeterminate results were reported as follows 1.4%,17% (2,3).
Some reasons are thought to effect the results. Ferrara et al. noted that indeterminate QFT-2G test results appeared in 21% of tests performed in routine clinical microbiological laboratories due to positive control failure and that indeterminate results were significantly overrepresented among patients receiving immunosuppressive treatments. However, there was no speculation concerning the reason (6). Banach found that age, race/ethnicity and sex were associated with high nil and low mitogen of indeterminate results (2%). Although technical factors relating to specimen handling and test performance may influence the indeterminate result rate, their data also showed that biological factors may also play a role (7).
Although it has been indicated that younger children (< 5 yrs old) also tend to show indeterminate QFT-2G test results, this group presented with a normal range of lymphocyte counts and serum protein (8).
There are studies mostly comparing IGRAs with tuberculin skin test in our country. As far as we know there is no data about indeterminate results published. We have a limitation in this study by only performing QFT-G in tube tests not also with T SPOT TB. So we couldnt compare these two IGRAs to show the correlation of age and the indeterminate results. The other limitation is this study is a retrospective one. To determine the scale there should be studies of large number patients.
Yazışma Adresi (Address for Correspondence)
Dr. Yeşim GÜROL
Yeditepe Üniversitesi Tıp Fakültesi,
Tıbbi Mikrobiyoloji Anabilim Dalı,
İSTANBUL - TÜRKİYE