Introduction: Sarcoidosis and tuberculosis (TB) are the diseases that share many similarities. Mycobacterium tuberculosis (MTB) culture results are the gold standard for the diagnosis of TB, but false positive results are not rare. The aim was to evaluate the utility of QFT in detecting latent TB infection in a group of sarcoidosis patients with negative history of TB and negative culture/BACTEC results, and checking sarcoidosis activity influence on the QFT results. Additionally, we assessed if QFT negative result may strengthen the suspicion that positive culture/BACTEC results are false positive.
Material and methods: 37 culture-negative and 6 culture-positive sarcoidosis patients were enrolled. On the basis of clinical and radiological data TB was considered unlikely (false-positive results). A control group consisted of age-matched subjects with excluded TB (n = 37). QuantiFERON-TB GOLD In-Tube (QIAGEN, USA) was used according to the manual. Test validity was checked basing on the results obtained from a low-risk (n = 21) and active TB group (n = 23).
Results: The frequency of positive results tended to be higher in MTB(-) sarcoidosis (24.3% vs. 13.5% for the control group, p = 0.37), but was similar to the general population. None of culture-positive sarcoidosis patients was QFT-positive. The positive results were equally distributed among patients with active and inactive sarcoidosis.
Conclusions: QFT has been found to be the useful test for the detection of latent TB infection in sarcoidosis patients. In addition, we confirm that sarcoidosis activity does not negatively influence the result of QFT. Moreover, QFT would be proposed as a cost-saving diagnostic test providing additional diagnostic information when false positive MTB culture result in the sarcoidosis patient is highly suspected. However, in each case clinical, radiological and epidemiological data should be considered before taking the therapeutic decision.
Keywords: IGRA; quantiferon test; sarcoidosis; tuberculosis.