Data analysis of the examination and clinical usefulness of T-SPOT in tuberculosis diagnosis

Abstract

The interferon-gamma release assays (IGRA) is an indispensable test for tuberculosis diagnosis in Japan, where many tuberculosis patients still exist. Analysis of results of T-SPOT, which is one type of IGRA, was conducted for about 4 years to verify its clinical usefulness. The determination results of 1,744 cases were as follows: negative, 90.8%; intermediate, 1.9%; positive; 5.8%; and indeterminate, 1.5%. The average age of patients with positive determination was 66.9 years. When comparing the determination results of T-SPOT with those of QuantiFERON (QFT), it was confirmed that there were many clear negative or positive determination results. After QFT was found to show intermediate or indeterminate determination, we examined the cases in which T-SPOT was conducted in the next test. Approximately 80% of the cases were found to be negative in the next T-SPOT after the intermediate determination using QFT, and about 95% were found to be negative in the next T-SPOT after the indeterminate determination using QFT. A comparison was made with acid-fast bacteria test carried out at the same time as T-SPOT. Among 58 patients with T-SPOT positive results, 12 had mycobacterium tuberculosis and 2 had nontuberculous mycobacteria. Mycobacterium tuberculosis was detected in 3 out of 294 T-SPOT negative patients, and 2 patients had taken steroid drugs. Since T-SPOT gives clear negative or positive determinations with few intermediate or indeterminate determinations in many cases, it is considered to be useful for the early diagnosis of tuberculosis. However, it is also necessary to judge the results on the basis of the fact that there are negative determinations in mycobacterium tuberculosis positive cases.