CHEST Clinical Utility of the QuantiFERON -2G Test for Elderly Patients With Active Tuberculosis* Yoshihiro Kobashi, MD, PhD; Keiji Mouri, MD; Shinich Yagi, MD; Yasushi Obase, MD, PhD; Naoyuki Miyashita, MD, PhD; Niro Okimoto, MD, PhD; Toshiharu Matsushima, MD, PhD; Takeshi Kageoka, MD, PhD; and Mikio Oka, MD, PhD Original Research TUBERCULOSIS Objective: To evaluate the response to the QuantiFERON--2 Gold (QFT-2G) test (Cellestis Ltd; Carnegie, VIC, Australia) in elderly patients with active tuberculosis () to determine whether the QFT-2G test might be a feasible method for diagnosing infection in this group of patients. Methods: The subjects were 30 elderly patients with active and 00 younger patients with active. The QFT-2G test results were analyzed in relation to combined and separate responses to early secretory antigenic target 6-kD (ESAT-6) protein and culture filtrate protein 0 (CFP-0) antigens. Results: Of the 30 elderly patients with active, 27% had a positive tuberculin skin test (TST) result and 77% had a positive QFT-2G test result. Of the 00 younger patients with active, 70% had a positive TST result and 87% had a positive QFT-2G test result. Although there was no significant difference between the two patient groups in the positive rate for the QFT-2G test results (p 0.85), there was a significant difference in the rates of positive TST results between the elderly and younger patients (p 0.02). The positive test result rate for both ESAT-6 and CFP-0 antigens in the elderly patients (7%) was significantly lower than that in younger patients (37%; p 0.038). There was an indeterminate result for the QFT-2G test in five elderly patients, and this might have been related to the presence of lymphocytopenia due to underlying disease. A negative result on the QFT-2G test was detected in two elderly patients, and this might have been related to the severity of the active. Conclusion: We confirmed that the QFT-2G test might be a more useful method of diagnosing infection than the TST for elderly patients if peripheral lymphocyte counts have been preserved. (CHEST 2008; 33:96 202) Key words: active tuberculosis; elderly patients; QuantiFERON -2G; tuberculin skin test Abbreviations: BCG bacillus Calmette-Guerin; CFP-0 culture filtrate protein 0; ESAT-6 early secretory antigenic target 6-kd; IFN interferon; M Mycobacterium tuberculosis; QFT-2G QuantiFERON--2 Gold; tuberculosis; TST tuberculin skin test Although the tuberculin skin test (TST) has frequently been performed as the standard immunologic diagnostic tool for diagnosing tuberculosis () infection in the 20th century, it does not reliably distinguish resulting either from previous immunization with the bacillus Calmette-Guerin (BCG) vaccine or from most nontuberculous mycobacteria. To replace the TST test, the availability of Mycobacterium tuberculosis (M) antigen-specific interferon (IFN)- release assays has represented a significant advance in the field of diagnosis. 2 4 These assays measure T-cell-induced IFN- responses in M-specific peptides derived from the early secretory antigenic target 6-kD (ESAT-6) protein and culture filtrate protein 0 (CFP-0). These antigens are encoded by the genetic region of difference that is present in all strains of M but is absent in nontuberculous mycobacteria and all BCG vaccine strains. The following two commercial IFN- assays have become available in the last few years: the QuantiFERON--2 Gold (QFT-2G) assay (Cellestis Ltd; Carnegie, VIC, Australia) with an enzyme-linked immunosorbent assay used to mea- 96 Original Research
sure IFN- concentrations in supernatants; and T-SPOT. (Oxford Immunotec; Oxon, UK) with an enzyme-linked immunospot assay used to detect individual T cells producing IFN-. 5,6 The US Food and Drug Administration has approved the QFT-2G test and is currently evaluating the T-SPOT. test, which has been approved for use in Europe. These tests demonstrate a positive result for most persons with active disease. Of these tests, although the QFT-2G test was first used commercially in Japan in April 2005 for the diagnosis of, the T-SPOT. test has not yet been approved in Japan. Therefore, we performed the QFT-2G test for elderly patients with active and compared findings with those of the TST test in this study. To date, although there have been many reports 7 0 about the clinical usefulness of the QFT-2G test for patients with infection or latent infection, it has been indicated that care is needed when diagnosing infection for young pediatric patients (ie, those 5 years old) or elderly patients. However, there have been few studies performing a detailed investigation of the clinical effectiveness for elderly patients (ie, those 80 years old) with active. Therefore, we evaluated the QFT-2G test responses in elderly patients with active to determine whether the QFT-2G test might be a feasible method for diagnosing infection in elderly patients (ie, those 80 years old) compared to that in younger patients (ie, those 80 years old) according to the combined and separate responses to ESAT-6 and CFP-0 antigens. Study Population Materials and Methods One hundred thirty patients including 30 elderly patients with active that had been confirmed by positive results of cultures *From the Division of Respiratory Diseases (Drs. Kobashi, Mouri, Yagi, Obase, Miyashita, and Oka), Department of Medicine, Kawasaki Medical School, Kurashiki, Japan; the Division of Respiratory Diseases (Dr. Okimoto), Department of Medicine, Kawasaki Medical School Kawasaki Hospital, Okayama, Japan; the Division of Respiratory Diseases (Dr. Matsushima), Kurashiki Daiichi Hospital, Oimatsuchou, Kurashiki, Japan; and the Department of Laboratory Division, Kurashiki Central Hospital, Kurashiki, Japan. The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article. Manuscript received August 7, 2007; revision accepted July 5, 2008. Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal. org/misc/reprints.shtml). Correspondence to: Yoshihiro Kobashi, Division of Respiratory Diseases, Department of Medicine, Kawasaki Medical School, 577 Matsushima, Kurashiki, 70-092, Japan; e-mail: yoshihiro@med. kawasaki-m.ac.jp DOI: 0.378/chest.07-995 of sputum, BAL fluid, pleural fluid, peritoneal fluid, or lymph node tissue samples were prospectively enrolled between April 2005 and June 2007. This study was approved by the ethics committee of each institution. The patients with active received their diagnoses at Kawasaki Medical School Hospital (,072 beds), Kawasaki Medical School Kawasaki Hospital (650 beds), Kurashiki Central Hospital (,570 beds), Kurashiki Daiichi Hospital (92 beds), or Asahigaoka Hospital (90 beds). We obtained written, informed consent from all patients in this study. All patients had either negative responses to serological tests for HIV or had no obvious risk factors for HIV infection. Subjects were divided into the following two groups: group consisted of 30 elderly patients ( 80 years old) with active ; and group 2 consisted of the remaining 00 younger patients ( 80 years old) with active. From patients in both groups with active, we collected demographic data regarding () any history of previous infection or antituberculous treatment, (2) other underlying diseases (ie, respiratory diseases such as healed pulmonary or COPD, and nonrespiratory diseases such as malignant disease, including leukemia, diabetes mellitus, renal failure with hemodialysis, collagen vascular disease, neurologic disease, GI disease, cardiovascular disease, and HIV infection), and (3) the receipt of immunosuppressive drugs within 3 months before enrollment into this study. Information regarding any previous Mantoux TST results and BCG vaccination inoculation, as well as information about laboratory findings (ie, WBC count, lymphocyte count, total protein concentration, and albumin concentration) and radiologic findings (ie, portion, extension, and cavity) were collected at the time of enrollment. Sputum or other appropriate respiratory samples were collected from all patients, and culture samples were obtained for the detection of mycobacteria. Sample Collection and TST Each patient in both groups had a heparinized blood sample collected by venipuncture for performing a whole-blood IFN- assay. Blood samples were collected before the administration of the Mantoux TST. For the TST test, 0. ml of tuberculin purified protein derivative (Nippon BCG Manufacturing; Tokyo, Japan [equivalent to three tuberculin units of purified protein derivative solution]) was injected intradermally into the volar aspect of the forearm, and the transverse induration diameter was measured 48 h later. The results of the test were interpreted by hospital staff based on the patient s degree of risk, according to current guidelines ; a lower cutoff of 5 mm for a positive test result was used for each patient. QFT-2G Test The QFT-2G test was performed according to the recommendations of the manufacturer, and the test result was judged according to the guidelines of the Centers for Disease Control and Prevention. 5 In brief, the test consisted of a negative control (a nil well [ie, whole blood without antigens or mitogen]), a positive control (a mitogen well [ie, whole blood stimulated with the mitogen phytohemagglutinin]), and two sample wells (ie, whole blood stimulated with either ESAT-6 or CFP-0). Wholeblood specimens were incubated for 8 h (overnight) at 37 C in a humidified atmosphere. The IFN- level of the nil well was considered to be the background value and subtracted from the values for the mitogen well and the antigen-stimulated wells. The test result was considered to be positive if the IFN- level in the sample well after stimulation with ESAT-6, and after the CFP-0 concentration was 0.35 IU/mL (after subtraction of the value for the nil well), irrespective of the result for the positive control well. The test was considered to be negative if www.chestjournal.org CHEST / 33 / 5/ MAY, 2008 97
the IFN- level was 0.35 IU/mL and the IFN- level of the positive control well was 0.5 IU/mL. The test result was considered to be indeterminate if the IFN- level was 0.35 IU/mL in both antigen wells and 0.5 IU/mL in the positive control well. Statistical Analysis Information from the questionnaires, TST results, and wholeblood IFN- assay results were entered into spread sheet software (Excel 2000; Microsoft; Redmond, WA) and then were transferred to a statistical software package (Stata, version 7.0 Stata Corp; College Station, TX) for statistical analysis. The Pearson 2 test was used to compare proportions in the two groups, and the McNemar test was used to compare paired proportions. The Mann-Whitney U test was used to compare unpaired results, and the Wilcoxon signed rank test was used to compare paired observations. Significance was recognized at p 0.05. Results Thirty elderly patients (ie, those 80 years old) with active (group ) and 00 younger patients (ie, those 80 years old) with active (group 2) were enrolled into this study between April 2005 and June 2007. The clinical diagnosis of the group patients was pulmonary in 22 patients (including pulmonary tuberculoma in 2 patients), tuberculous pleuritis in 4 patients, miliary in 2 patients, tuberculous lymphadenitis in patient, and pulmonary plus tuberculous pleuritis in patient. The clinical diagnosis of the patients in group 2 was pulmonary in 59 patients (including pulmonary tuberculoma in 8 patients), tuberculous pleuritis in 4 patients, tuberculous lymphadenitis in 2 patients, pulmonary and tuberculous pleuritis in 8 patients, miliary in 5 patients, and tuberculous peritonitis in 2 patients. There was no significant difference in the clinical diagnoses between the two groups. Thirty patients in group were confirmed as being positive for M by cultures of samples of sputum (3 patients with pulmonary and patient with pulmonary tuberculoma), BAL fluid (7 patients with pulmonary, 2 patients with miliary, and patient with pulmonary tuberculoma), pleural fluid (4 patients with tuberculous pleuritis and patient with pulmonary and tuberculous pleuritis), resected lymph node ( patient with cervical tuberculous lymphadenitis). Acid-fast smear results for sputum, bone marrow, BAL fluid, pleural or peritoneal fluid, or lymph node samples were positive in 4 of 30 patients (47%) in group. The remaining 6 patients had negative results for acidfast smear and positive results for cultures for. One hundred patients in group 2 were confirmed as being positive for M by cultures of samples of sputum (32 patients with pulmonary, 6 patients with pulmonary and tuberculous pleuritis, and 2 patients with pulmonary tuberculoma), BAL fluid (9 patients with pulmonary, 6 patients with pulmonary tuberculoma, and 5 patients with miliary ), pleural fluid (4 patients with tuberculous pleuritis and 2 patients with pulmonary and tuberculous pleuritis), resected lymph node (2 patients with cervical tuberculous lymphadenitis), peritoneal fluid (2 patients with tuberculous peritonitis). Acid-fast smear results for samples were positive in 54 of 00 patients (54%) in group 2. The remaining 46 patients had negative acid-fast smear results and positive culture results for. The clinical characteristics of both groups are shown in Table. Compared to group 2, group had Table Clinical Characteristics of 30 Elderly Patients ( ) and 00 Younger Patients ( 2)* (n 30) 2 (n 00) Clinical Characteristics Pulmonary (n 22) Extrapulmonary (n 8) Both (n 30) Pulmonary (n 59) Extrapulmonary (n 4) Both (n 00) p Value Age, yr 83.7 5.8 8.8 6.0 82.4 5.6 62. 2.2 60.7 2.0 6.3 2. 0.00 Sex 0.582 Male 8 6 24 45 3 76 Female 4 2 6 4 0 24 Smoking history 5 (68) 6 (75) 2 (70) 38 (64) 26 (63) 64 (64) 0.804 Alcohol abuse history 4 (8) (3) 5 (7) (9) 7 (7) 8 (8) 0.95 Underlying disease 22 (00) 8 (00) 30 (00) 39 (66) 25 (6) 64 (64) 0.03 Respiratory disease 9 (4) 3 (38) 2 (40) 8 (3) 3 (32) 3 (3) 0.93 Nonrespiratory disease 3 (59) 5 (62) 8 (60) 2 (35) 2 (29) 33 (33) 0.023 Immunosuppressive treatment 2 (9) (3) 3 (0) 6 (0) 4 (0) 0 (0) 0.960 Received BCG vaccination 3 (59) 5 (63) 8 (60) 37 (63) 24 (59) 6 (6) 0.890 Received treatment 4 (8) 2 (25) 6 (20) 0 (7) 6 (5) 6 (6) 0.86 *Values are given as the mean SD or No. (%), unless otherwise indicated. All patients received corticosteroid therapy. 98 Original Research
Table 2 Comparison Between the Results of TST and QFT-2G Test Among 30 Elderly Patients With Active Disease ( ) and 00 Younger Patients With Active Disease ( 2)* QFT-2G Test Result TST Result Positive Negative Total 2 2 2 Positive 27 70 50 7 77 87 Negative 0 0 7 4 7 4 Indeterminate 0 0 7 9 7 9 Total 27 70 74 30 00 00 *Values are given as %. Table 4 Comparison of the Results of QFT-2G Test Analyzed by Combined and Separate Responses to ESAT-6 and CFP-0 Antigens Between Elderly Patients ( ) and 00 Younger Patients ( 2)* QFT-2G Test (n 30) 2 (n 00) Total (n 30) p Value ESAT-6 protein 0 (33) 28 (28) 38 (29) 0.08 only positive CFP-0 only 9 (30) 27 (27) 36 (28) 0.740 positive ESAT-6 protein and 4 (3) 32 (32) 36 (28) 0.038 CFP-0 positive Total 23 (77) 87 (87) 0 (85) *Values are given as No. (%), unless otherwise indicated. a significantly higher percentage of patients with underlying disease, especially nonrespiratory disease. Concerning the laboratory data and chest radiologic findings in the two groups, there were no significant differences in the indicators of immune status, such as peripheral lymphocyte counts or albumin concentrations, nutritional condition, extension of the lesion, or the existence of a cavity. Comparisons between the results of the TST and the QFT-2G test among 30 elderly patients and 00 younger patients with active are shown in Table 2. Elderly patients with active had a significantly higher rate of positive QFT-2G test results (76%) than of positive TST results (27%). However, younger patients with active did not show any significant difference between the positive rate on QFT-2G test results (87%) and the positive rate on TST results (70%). A comparison of the results of the TST and QFT-2G test, including the range and median of the maximum diameter of induration of the TST or those of IFN- levels of the QFT-2G test between elderly patients and younger patients, is shown in Table 3. Although group had a significantly lower positive result rate (27%) and lower values for positive results than group 2 (70%) on the TST test, there was no significant difference in the positive rate and the values for positive results on QFT-2G test between group (76%) and group 2 (87%). As for the QFT-2G test, negative findings were more frequent in group (two patients; 7%) than in group 2 (four patients; 4%), but there was no significant difference. The indeterminate result also occurred more frequently in group (five patients; 6%) than in group 2 (nine patients; 9%), but there was no significant difference. A comparison of QFT-2G test results that were analyzed according to the combined and separate responses to ESAT-6 and CFP-0 antigens between the elderly patient group (group ) and the group of 00 younger patients (group 2) is shown in Table 4. Although there was no significant difference in the rate of positive response to ESAT-6 protein antigen only (p 0.08) or CFP-0 antigen only (p 0.740) between the two groups, the positive response rate to ESAT-6 protein and CFP-0 antigens in group (3%) was significantly lower than that in group 2 (32%; p 0.038). The clinical findings of elderly patients with active who had false-negative or indeterminate Table 3 Comparison of the Results of TST and QFT-2G Test Between 30 Elderly Patients ( ) and 00 Younger Patients ( 2)* Test Results (n 30) 2 (n 00) Total (n 30) p Value TST Positive 8 (27) approximately 5 30 mm; 2 mm 70 (70) approximately 5 65 mm; 25 mm 78 (60) 0.02 (0.04) Negative 22 (73) 30 (30) 52 (40) 0.03 QFT-2G test Positive 23 (77) approximately 0.38 5.20 IU/mL; 87 (87) approximately 0.42 7.85 IU/mL; 0 (85) 0.85 (0.64).03 IU/mL.20 IU/mL Negative 2 (7) 4 (4) 6 (5) 0.44 Indeterminate 5 (7) 9 (9) 4 (0) 0.02 *Values are given as No. (%) range; median, unless otherwise indicated. Values in parenthesis are for comparisons of the positive response rates. www.chestjournal.org CHEST / 33 / 5/ MAY, 2008 99
QFT-2G test results are shown in Table 5. Although two patients showed false-negative results on the QFT-2G test as well as on the TST, these were both immunocompromised patients with severe underlying disease, and lymphocytopenia was recognized in the peripheral blood of these patients, although nutritional conditions such as total protein or albumin level were comparatively preserved. In one case, the sputum specimen was smear negative and culture positive ( colony at 8 weeks) for on bacteriologic findings, and showed slight extension of the lesion without cavity on radiologic findings. In the other case, pleural effusion was smear negative and culture positive ( colony at 8 weeks) for on bacteriologic findings, and tuberculous pleuritis was diagnosed. While five patients showed indeterminate results on the QFT-2G test, these five also had various underlying diseases, and lymphocytopenia was recognized in the peripheral blood of these patients. Furthermore, nutritional conditions were extremely poor in most of these patients. However, all five patients showed negative results on serologic tests for HIV. Regarding the judgment of the QFT-2G test, two patients were considered to have had negative responses because the positive control of the QFT-2G test was 0.5 IU/mL. Five patients were considered to have indeterminate results because the positive control for the QFT-2G test was 0.5 IU/mL. Otherwise, four patients in group 2 showed negative results on the QFT-2G test due to severe underlying diseases and lymphocytopenia, as well as negative results on the TST (the positive control of the QFT-2G test was 0.5 IU/mL). Nine patients in group 2 showed indeterminate results on the QFT-2G test due to various underlying diseases and lymphocytopenia, as well as negative results on the TST (the positive control for the QFT-2G test was 0.5 IU/mL). Discussion Whereas the sensitivity of the QFT-2G test for detecting infection in patients with untreated culture-confirmed was approximately 80% in previous studies, 7,9 its sensitivity for detecting infection in younger pediatric patients ( 5 years old), elderly patients, or immunocompromised patients has not yet been determined. Recently, Detjen et al 2 reported that IFN- release assays (both the QFT-2G and T-SPOT. tests) are useful for diagnosing disease in young children. Luetkemeyer et al 3 and Rangaka et al 4 reported that these assays were useful tests for diagnosing in immunocompromised patients with HIV infection. However, there have been few reports investigating in detail Table 5 Clinical Findings of Elderly Patients With Active Disease Who Had False-Negative or Indeterminate QFT-2G Test Results* Clinical Diagnosis Chest Radiograph Finding AFB Smear Result/ Culture Result (Culture Specimen) TST Result HIV Status Lymphocyte Count, cells/ L WBC Count, cells/ L Alb, mg/dl TP, mg/dl Underlying Disease Age, yr/sex QFT-2G Test Result Patient No. 6.4 3.0 5,400 328 / (Sputum) Right cavity ( ) Pulmonary Negative 82/M Rheumatoid lung 6.7 3.3 6,800 544 / (PE) Left PE Tuberculous pleuritis 2 Negative 80/M Diabetes mellitus Pulmonary 5.5 2.7 4,700 282 / (Sputum) Bilateral cavity ( ) 3 Indeterminate 89/M Lung cancer Pulmonary 4 Indeterminate 85/F CVD 5.0 2. 5,840 75 / (BALF) Bilateral cavity ( ) 5 Indeterminate 83/M MDS 6.0 2.6 2,640 84 / (Sputum) Left cavity ( ) Pulmonary 6 Indeterminate 80/M Gastric 6.4 3.2 3,600 280 / (BALF) Right cavity ( ) Pulmonary ulcer 7 Indeterminate 87/M OMI 6.5 3. 5,400 324 / (Sputum) Bilateral Pulmonary cavity ( ) *AFB acid-fast bacilli; BALF BAL fluid; CVD cerebrovascular disease; MDS myelodysplastic syndrome; PE pleural effusion; F female; M male; negative; positive; TP total protein; Alb albumin. Data denote portion and cavity finding. Treated with corticosteroid therapy. 200 Original Research
the clinical usefulness of these tests for elderly patients (ie, those 80 years old) with active. Concerning the QFT-2G test result and the TST result stratified by age, Mori et al 7 reported that while the positive result rates on the QFT-2G test and the TST were 92.3% and 54.5%, respectively, for 3 and patients (approximately 7 to 80 years old), those on the QFT-2G test and the TST were 80.0% and 6.7%, respectively, for 0 and 6 elderly patients (ie, those 80 years old). That is, the positive result rate on the TST was strikingly decreased in elderly patients with active who were 80 years old. Concerning this finding, we investigated the usefulness of the QFT-2G test as a supportive method for diagnosing infection in elderly patients (ie, those 80 years old) compared to that in younger patients ( 80 years old) in this study. Subsequently, although 27% of elderly patients with active had a positive TST result and 77% of this group had a positive QFT-2G result, and there was a significant difference between the results of the TST and THE QFT-2G test, 70% of younger patients with active had a positive TST result and 87% had a positive QFT-2G test result. Furthermore, there was no significant difference between TST test and QFT-2G test results in younger patients. Our findings resembled those reported by Mori et al. 7 This study confirmed that the QFT-2G test is a useful method for diagnosing infection compared to the TST even for elderly patients (ie, those 80 years old). Concerning the combined and separate responses to ESAT-6 protein and CFP-0 antigens in the QFT-2G test, the positive rate for response to both ESAT-6 protein and CFP-0 antigens in elderly patients with active was significantly lower than that in younger patients with active. Chee et al 5 reported that 47% of patients were positive for CFP-0 only, 20% of patients were positive for ESAT-6 protein only, and 33% of patients were positive for both antigens when the results were analyzed using combined and separate responses to ESAT-6 protein and CFP-0 antigens in 226 adults suspected of having latent infection by results of the T-SPOT. assay. The roles of ESAT-6 protein and CFP-0 in pathogenesis have not been yet defined. The genes encoding these antigens are transcribed together 6 ; these two proteins form a tight : complex, and evidence suggests that they are active as a complex. 7 As the reason underlying the low positive response rate for both antigens, it may be speculated that the dose of IFN- produced by M-specific antigens such as those for ESAT-6 protein and/or CFP-0 gradually decreases with aging. However, although we adopted the Centers for Disease Control and Prevention guidelines 5 for cutoff values indicating a positive response on the QFT-2G test (ie, levels of either ESAT-6 protein or CFP-0 antigen of 0.35 IU/mL), there was no problem in judging the results of QFT-2G tests for elderly patients with active because the positive rate on the QFT-2G test was significantly higher than that on the TST. Next, we investigated the reason for indeterminate QFT-2G test results in five patients with active and the false-negative QFT-2G test results for two patients with active as well as negative TST results in elderly patients with active. This finding was the same in younger patients with active. These results may become parameters that are linked with negative results on the TST in both groups. All five patients with indeterminate QFT-2G test results showed severe lymphocytopenia (ie, peripheral lymphocyte counts of 500/ L) due to underlying diseases or aging (Table 5). This QFT-2G test depends on the elaboration of inflammatory cytokines by T cells previously sensitized to Mspecific antigens. In this test, mononuclear cells from peripheral blood are stimulated in vitro, and the production of IFN- from sensitized T cells is measured by the enzyme-linked immunosorbent assay method. 2 Therefore, we considered that lymphocytopenia caused a decrease in the production of IFN- and lower mitogen QFT-2G test levels (ie, 0.5 IU/mL). Although there were two patients showing negative QFT-2G results, these patients both showed mild lymphocytopenia (ie, peripheral lymphocyte counts of approximately 300 to 600 IU/mL), differing from the five patients with indeterminate responses to the QFT-2G test. We speculate that the reason for the negative response to the QFT-2G test mainly related to the limited dose of M in the sputum culture, the small lesion size, or the presence of tuberculous pleuritis as extrapulmonary rather than lymphocytopenia. In conclusion, this study demonstrated the usefulness of the QFT-2G test as an immunologic diagnostic method for the detection of elderly patients (ie, those 80 years old) with active compared with the TST. However, because several indeterminate QFT-2G test results were encountered among patients with active who demonstrated moderateto-severe lymphocytopenia due to underlying diseases and a few negative QFT-2G test results were encountered in patients with active showing a limited dose of M in the sputum culture, small lesion size, or the presence of tuberculous pleuritis as extrapulmonary, we must take care to identify such patients among elderly patients (ie, those 80 years old) at the time the QFT-2G test is performed in order to obtain an accurate diagnosis of active. www.chestjournal.org CHEST / 33 / 5/ MAY, 2008 20
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