False negative results of QuantiFERON TB-2G test in patients with active tuberculosis

Ten of 140 patients (7.1%) showed negative results on a QFT-2G test. The 10 patients consisted of seven males and three females (mean age: 66.0 years old). Three of the 10 patients had no clinical symptoms and no underlying diseases. They showed negative results on the QFT-2G test repeatedly within 1 month and a negative response on a tuberculin skin test (TST). Six of the seven remaining patients were of advanced age, and all of them had underlying diseases. Although all seven patients showed negative results on the QFT-2G test repeatedly within 1 month, one of them showed a negative response on TST. The lymphocyte count was within the normal range in three patients with nutritional conditions. Although five of nine patients with pulmonary tuberculosis had cavitary lesions, six had lesions within one-third of the unilateral lung field. The clinical effect in all patients was good. We suspect that there are two patterns by which false negative results are shown on QFT-2G tests; one pattern involves the decrease of interferon-gamma production due to advanced patient age or lymphocytopenia, and in the other lymphocytes cannot produce interferon-gamma for Mycobacterium tuberculosis-specific antigen in young patients without underlying disease.