ResultsOf the 66 patients, the initial IGRA was positive in 24.2%, negative in 65.2%, and indeterminate in 10.6%. Forty-six patients (69.7%) showed consistent IGRA results during follow-up, and 13 patients (19.7%) had consistently positive results.

• Serial Igra Vse Serii

IGRA conversion rate was 12.1% (8/66) and reversion rate was 4.5% (3/66). Conversion of IGRA results was only observed in ankylosing spondylitis patients, and the median interval between the two tests in patients with conversion was 8.5 months. The mean IFN-γ level in the group of patients with consistently positive IGRA results was higher than that in the group with inconsistently positive results, although this trend was not statistically significant ( P=0.293). Indeterminate results were observed most frequently in patients with systemic lupus erythematosus.

Study populationsFrom September 2006 to November 2010, 276 patients who were consecutively referred by the rheumatology department to the immunology laboratory of Dong-A University Hospital for an IGRA were initially enrolled in this study. Of these, 69 patients (25.0%) had serial IGRA results.

A total of 210 specimens were obtained from these 69 patients. Patient charts were reviewed for demographic information, clinical diagnosis, medication information, previous TB history, blood cell count, IFN-γ levels measured by the IGRA assay, and the results of TST. Rheumatic diagnoses were determined by specialist clinicians.

Serial Igra Vse Serii

Among these 69 patients, 66 patients with rheumatic inflammatory disease who were treated with immunosuppressive agents were included in this study. Three patients, of whom two had fever of unknown origin and one had Kikuchi disease, were not treated with immunosuppressive agents, and therefore were excluded from the study. Interferon-gamma release assayA total of 66 patients who received immunosuppressive agents were serially screened using the QFT-G assay or QFT-GIT assay. The QFT-G test (Cellestis Limited, Carnegie, Victoria, Australia) was performed according to the manufacturer's recommendations. Briefly, four aliquots of heparinized whole blood were incubated with early secretory antigenic target-6 (ESAT-6), culture filtrate protein 10 (CFP-10), mitogen, and nil (i.e., saline) antigens. Following 12-18 hr of incubation at 37℃ in a humidified atmosphere, the plasma was aspirated from each well, and the amount of IFN-γ was measured by ELISA. For an ELISA run to be valid, the following performance criteria had to be fulfilled: a variation coefficient 0.98.

ELISA data were converted to IU/mL using the IFN-γ standard curve generated for each ELISA plate. IFN-γ values were calculated by subtracting the value obtained with nil antigens, with a cutoff value of 0.35 IU/mL according to the manufacturer's instructions. The result of QFT-G was interpreted as indeterminate if the IFN-γ level was 0.7 IU/mL, the result was indeterminate when the IFN-γ level was. Statistical analysisStatistical analyses were conducted using MedCalc version 9.3 (MedCalc Software, Mariakerke, Belgium).

Concordance between serial tests was assessed using kappa (κ) coefficients. The mean levels of IFN-γ in the different patient groups with initially positive IGRA results, and the differences in WBC, neutrophil, and lymphocyte counts between disease groups were compared by Kruskal-Wallis and Mann-Whitney tests.

Fisher's exact test was used to compare the frequency of indeterminate results of IGRA according to disease group.Twelve patients were treated for LTBI based on the positive tuberculin skin test; †Eight patients with IGRA conversion and one patient with IGRA reversion were included.Abbreviations: IGRA, interferon-gamma release assay; LTBI, latent tuberculosis infection.The mean time interval between IGRA tests was 9.2 months (range 1-38), and the mean IGRA test number was 3.1 (range 2-7). Thirty-one (47%) of the 66 patients received only two IGRA tests, and 16 patients (24.2%) received three tests. Two of the AS patients had six consecutive positive IGRA results and seven consecutive negative IGRA results, respectively. According to disease group, the mean number of IGRAs was 3.6 (range 2-7) for AS patients, 2.3 (range 2-3) for RA, 2.4 (range 2-4) for systemic lupus erythematosus (SLE), and 2.3 (range 2-3) for other diseases. Agreement between serial IGRAs and different types of IGRAA total of 203 IGRAs were performed. The initial IGRA result was positive in 16 patients (24.2%), negative in 43 (65.2%), and indeterminate in seven (10.6%).

Forty-six patients(69.7%) showed consistent IGRA results during follow-up. Agreement between results of the initial IGRA and those of the second IGRA was 69.7%, with a κ coefficient of 0.460 (95% confidence interval, 0.267-0.653). The percentage of consistent results from patients who had been tested with both QFT-G and QFT-GIT (26/37, 70.3%) was similar to that of patients tested with QFT-G only (12/16, 75.0%) and that of patients tested with QFT-GIT only (8/13, 61.5%). Conversion and reversion rates in serial IGRAThe IGRA conversion rate was 12.1% (8/66) and the reversion rate was 4.5% (3/66). Conversion was only observed in AS patients (8/39, 20.5%). Among patients who received TNF-α antagonists, six of the eight non-AS patients showed consistently negative IGRA results. One patient of the remaining two had consistently positive IGRA results and the other patient had consistently indeterminate results.

The median interval between two tests in patients with conversion was 8.5 months (range 6-27). There were two patients who had showed consecutive conversion and reversion during follow-up. One of the eight patients with conversion showed reversion after two consecutive positive results, and one of the three patients with reversion had a second positive result after three consecutive negative results. The mean level of IFN-γ response in the group with consistently positive IGRA results was higher than that in the groups with conversion or reversion, although the differences were not statistically significant ( and ). Frequency of indeterminate results according to disease groupOverall, indeterminate IGRA results were observed in 19/203 tests (9.4%).

Of the 66 patients, 13 (19.7%) showed at least one indeterminate result, and four of these 13 patients had consistently indeterminate results. The percentage of indeterminate IGRA results differed significantly according to disease group, and was highest among patients with SLE (8/11, 72.7%). The mean lymphocyte count of SLE patients (850/µL) was the lowest among the disease groups ( P. DISCUSSIONInvestigation of LTBI in patients treated with immunosuppressive agents is important because such patients are at increased risk of LTBI reactivation. Although it is common practice to screen patients for LTBI prior to commencement of TNF-α antagonist therapy , guidelines for subsequent monitoring of LTBI in patients receiving immunosuppressive agents, including TNF-α antagonists, have not been established. Monitoring of LTBI risk with IGRA has several advantages, including superior specificity compared to TST, as demonstrated in the case of patients vaccinated with BCG, as well as avoidance of a second visit and subjective variability in TST results.

In our study, we assessed the performance of the IGRA in serial testing for LTBI in patients with rheumatic disease undergoing treatment with immunosuppressive agents. Our study shows that the initial results of IGRA are in fair agreement with those of follow-up IGRA during immunosuppressive therapy in a country with an intermediate TB burden. IGRA conversion was observed in eight patients (12.1%) who received TNF-α antagonists, and was only observed in AS patients (20.5%). Among patients who received TNF-α antagonists, six of eight non-AS patients showed consistently negative IGRA results, and the remaining two patients had consistently positive results and consistently indeterminate results, respectively. The reason for the occurrence of IGRA conversion only in AS patients is uncertain, although a previous study reported that the TST conversion rate was significantly higher in AS patients than in RA patients, when both groups received TNF-α antagonists. In 27 RA patients in Taiwan who had completed a 12-month period of therapy with TNF-α antagonists, conversion of QFT-G was not observed.

In our study, the median interval between two tests in patients with conversion was 8.5 months, which is a relatively short period. Further studies are needed to establish the most appropriate follow-up interval for IGRA in patients treated with TNF-α antagonists. The conversion rate of IGRA may differ according to disease group and duration of follow-up. Further studies would also clarify the factors affecting IGRA conversion.Among patients with positive IGRA results, nearly 20% (13/66, 19.7%) had consistently positive results.

The mean level of IFN-γ response in consistently IGRA-positive patients was higher than that in patients with IGRA reversion, indicating that results showing a low positive IFN-γ response tend to be inconsistent. Two (3.0%) of the 66 patients showed both conversion and reversion in our study.

Similar results were reported from a study of the reproducibility of QFT-GIT in a targeted US screening population. In that study, transient responses to QFT-GIT were common; therefore, it was concluded that low positive IFN-γ results (.