Clinical Reevaluation of the QuantiFERON TB-2G Test as a Diagnostic Method for Differentiating Active Tuberculosis from Nontuberculous Mycobacteriosis

When and how to treat pulmonary non-tuberculous mycobacterial diseases

Non-tuberculous mycobacteria are ubiquitous environmental organisms that have been recognized as a cause of pulmonary infection for over 50 years. Traditionally patients have had underlying risk factors for development of disease; however, the proportion of apparently immunocompetent patients involved appears to be rising. Not all patients culture-positive for mycobacteria will have progressive disease, making the diagnosis difficult, though criteria to aid in this process are available. The two main forms of disease are cavitary disease (usually involving the upper lobes) and fibronodular bronchiectasis (predominantly middle and lingular lobes). For patients with disease, combination antibiotic therapy for 12-24 months is generally required for successful treatment, and this may be accompanied by drug intolerances and side-effects. Published success rates range from 30% to 82%. As the progression of disease is variable, for some patients, attention to pulmonary hygiene and underlying diseases without immediate antimycobacterial therapy may be more appropriate. Surgery can be a useful adjunct, though is associated with risks. Randomized controlled trials in well-described patients would provide stronger evidence-based data to guide therapy of non-tuberculous mycobacteria lung diseases, and thus are much needed.

Guidelines on the diagnosis and treatment of pulmonary non-tuberculous mycobacteria infection

While the prevalence of Mycobacterium tuberculosis continues to decline in the developed world, the same cannot be said for non-tuberculous mycobacteria (NTM). These organisms are increasing in incidence and prevalence throughout the world. This is probably because of a combination of increased exposure, improved diagnostic methods and an increase in the prevalence of risk factors that predispose individuals to infection. Considerable confusion can arise in determining in the wide range of species whether an isolated NTM is in fact a contaminant or a pathogenic organism when isolated in sputum or bronchoalveolar lavage. This confusion combined with increasing requests for advice on the treatment of disease has led to the development of guidelines to assist the clinician in diagnosing and treating infection accurately.

Systematic review: T-cell-based assays for the diagnosis of latent tuberculosis infection: an update

BACKGROUND

Interferon-gamma-release assays (IGRAs) are alternatives to the tuberculin skin test (TST). A recent meta-analysis showed that IGRAs have high specificity, even among populations that have received bacille Calmette-Guérin (BCG) vaccination. Sensitivity was suboptimal for TST and IGRAs.

PURPOSE

To incorporate newly reported evidence from 20 studies into an updated meta-analysis on the sensitivity and specificity of IGRAs.

DATA SOURCES

PubMed was searched through 31 March 2008, and citations of all original articles, guidelines, and reviews for studies published in English were reviewed.

STUDY SELECTION

Studies that evaluated QuantiFERON-TB Gold, QuantiFERON-TB Gold In-Tube (both from Cellestis, Victoria, Australia), and T-SPOT.TB (Oxford Immunotec, Oxford, United Kingdom) or its precommercial ELISpot version, when data on the commercial version were lacking. For assessing sensitivity, the study sample had to have microbiologically confirmed active tuberculosis. For assessing specificity, the sample had to comprise healthy, low-risk individuals without known exposure to tuberculosis. Studies with fewer than 10 participants and those that included only immunocompromised participants were excluded.

DATA EXTRACTION

One reviewer abstracted data on participant characteristics, test characteristics, and test performance from 38 studies; these data were double-checked by a second reviewer. The original investigators were contacted for additional information when necessary.

DATA SYNTHESIS

A fixed-effects meta-analysis with correction for overdispersion was done to pool data within prespecified subgroups. The pooled sensitivity was 78% (95% CI, 73% to 82%) for QuantiFERON-TB Gold, 70% (CI, 63% to 78%) for QuantiFERON-TB Gold In-Tube, and 90% (CI, 86% to 93%) for T-SPOT.TB. The pooled specificity for both QuantiFERON tests was 99% among non-BCG-vaccinated participants (CI, 98% to 100%) and 96% (CI, 94% to 98%) among BCG-vaccinated participants. The pooled specificity of T-SPOT.TB (including its precommercial ELISpot version) was 93% (CI, 86% to 100%). Tuberculin skin test results were heterogeneous, but specificity in non-BCG-vaccinated participants was consistently high (97% [CI, 95% to 99%]).

LIMITATIONS

Most studies were small and had limitations, including no gold standard for diagnosing latent tuberculosis and variable TST methods and cutoff values. Data on the specificity of the commercial T-SPOT.TB assay were limited.

CONCLUSION

The IGRAs, especially QuantiFERON-TB Gold and QuantiFERON-TB Gold In-Tube, have excellent specificity that is unaffected by BCG vaccination. Tuberculin skin test specificity is high in non-BCG-vaccinated populations but low and variable in BCG-vaccinated populations. Sensitivity of IGRAs and TST is not consistent across tests and populations, but T-SPOT.TB appears to be more sensitive than both QuantiFERON tests and TST.

QuantiFERON®-TB Gold in the Diagnosis of Active Tuberculosis

QuantiFERON®-TB Gold (QFT) is an indirect diagnostic test for latent tuberculosis (TB) infection and active TB. This study aimed to evaluate and compare QFT and the tuberculin skin test (TST) for the diagnosis of active TB disease, not bacteriologically verified at the time of therapy initiation. Seventy-three patients with suspected active TB were examined. Further diagnostic steps confirmed the diagnosis of active TB in 53 persons. QFT was positive in 43 persons (81%), negative in seven (13%), and indeterminate results were found in three (6%). The sensitivity of the test was 86% in those with valid results, significantly higher than that for the TST (62%), and the correlation between the two tests was not high (55%). The QFT test is a useful addition to existing methods for the diagnosis of active TB.

Clinical utility of the QuantiFERON TB-2G test for elderly patients with active tuberculosis

OBJECTIVE

To evaluate the response to the QuantiFERON-TB-2 Gold (QFT-2G) test (Cellestis Ltd; Carnegie, VIC, Australia) in elderly patients with active tuberculosis (TB) to determine whether the QFT-2G test might be a feasible method for diagnosing TB infection in this group of patients.

METHODS

The subjects were 30 elderly patients with active TB and 100 younger patients with active TB. 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 10 (CFP-10) antigens.

RESULTS

Of the 30 elderly patients with active TB, 27% had a positive tuberculin skin test (TST) result and 77% had a positive QFT-2G test result. Of the 100 younger patients with active TB, 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 = 0.185), there was a significant difference in the rates of positive TST results between the elderly and younger patients (p = 0.012). The positive test result rate for both ESAT-6 and CFP-10 antigens in the elderly patients (17%) 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 TB.

CONCLUSION

We confirmed that the QFT-2G test might be a more useful method of diagnosing TB infection than the TST for elderly patients if peripheral lymphocyte counts have been preserved.

Long-term follow-up of the QuantiFERON TB-2G test for active tuberculosis disease

OBJECTIVE

To evaluate transitional changes in QuantiFERON TB-2G (QFT-2G) test results in the serial testing on the same patients and to reevaluate the optimal threshold of positive response of QFT-2G test as a cure of TB infection.

METHODS

We prospectively investigated transitional changes of QFT-2G test results in 22 patients with active tuberculosis (TB) over three years after the initiation of treatment with antituberculosis drugs. Treatment using antituberculosis drugs was performed for six months in all patients.

RESULTS

The positive rate of QFT-2G test results decreased 50% at the treatment completion. Thereafter, although the positive rate of QFT-2G test results has been decreased 45% six months later even if treatment was finished, it decreased slightly to 41% two years later and 36% three years later. If the cut-off value was situated below 50% (IFN-gamma level three years later/ IFN-gamma level of baseline peak value), we could judge the conversion of QFT-2G test in most cases except for two cases three years after the initiation of antituberculosis treatment through this study.

CONCLUSION

It may be difficult to monitor markers in the cure of TB infection using QFT-2G tests. The cut-off level for a positive response on QFT-2G test may need to be reconsidered when the test is used to monitor the response of active TB to therapy.

An indeterminate QuantiFERON TB-2G response for miliary tuberculosis, due to severe pancytopenia

We report the case of a 56-year-old man with miliary tuberculosis whose response to the QuantiFERON (QFT) TB-2G (Cellestis; South Melbourne, Australia) test was indeterminate due to pancytopenia (lymphocytopenia). The patient had severe lymphocytopenia due to either the miliary tuberculosis or immunosuppressive treatment with a corticosteroid; for the 2 years before admission, he had received corticosteroid treatment for Behçet's disease. The lymphocytopenia was also a complication of multiple organ failure and disseminated intravascular coagulation. A chest radiograph and computed tomography (CT) scan revealed a miliary shadow. After intubation performed because of acute respiratory failure, Mycobacterium tuberculosis was cultured from bronchoalveolar lavage fluid. We made a clinical diagnosis of miliary tuberculosis because M. tuberculosis was demonstrated in both lung and bone marrow specimens. However, immunologically, the tuberculin skin test was negative and the QFT-TB 2G test response was indeterminate, based on the CDC guideline. Although the QFT-TB 2G test has been used recently as a supportive method for the diagnosis of active tuberculosis, care must be taken in judging the condition of a patient with lymphocytopenia caused by severe underlying disease or immunosuppressive treatment. This patient was treated with antituberculous drugs 3 days after admission, but he died of multiple organ failure 6 days after admission.

Use of the QuantiFERON-TB Gold test in Japanese patients with sarcoidosis

BACKGROUND AND OBJECTIVE

Mycobacterium tuberculosis has been proposed as a candidate agent for the cause of sarcoidosis. The QuantiFERON-TB Gold test has a higher specificity for detecting M. tuberculosis infection than the conventional tuberculin skin test. This study aimed to investigate the rate of positive QuantiFERON-TB Gold results in Japanese sarcoidosis patients.

PATIENTS AND METHODS

The QuantiFERON-TB Gold test, an enzyme-linked immunosorbent assay, was used to assess the levels of interferon-gamma resulting from immune responses to M. tuberculosis-specific antigens, namely early secretory antigen target 6 and culture filtrate protein 10, in 90 Japanese sarcoidosis patients.

RESULTS

The QuantiFERON-TB Gold result was positive in 3 of the 90 patients tested.

CONCLUSION

The positivity rate of QuantiFERON-TB Gold was 3.3% in Japanese sarcoidosis patients.

[Interferon-gamma release assays in tuberculosis diagnostics]

Two years ago, CE certified interferon-gamma release assays (IGRA) were launched on the German market (QuantiFERON-TB Gold In-Tube and T-SPOT-TB). Since this time, a multitude of studies have analysed these assays. Guidelines have been elaborated by national expert committees of England, the USA and Switzerland. However, standards of tuberculosis diagnostics and management may vary from country to country. This statement provides practice relevant recommendations for indications, pre-analytics and the interpretation of IGRA test results under different clinical conditions. The IGRA are integrated into existing guidelines for the management of tuberculosis.

Usefulness of QuantiFERON TB-2G, a diagnostic method for latent tuberculosis infection, in a contact investigation of health care workers

OBJECTIVE

To evaluate the usefulness of QuantiFERON TB-2G (QFT-2G) for detecting latent tuberculosis infection (LTBI) in a contact investigation of health care workers.

METHODS

The investigated subjects were 190 subjects among the health care workers who were examined between January 2005 and June 2006. Background information, including a past history of tuberculosis (TB) or tuberculin skin test (TST) or BCG vaccination, and contact score (infectivity x contact duration) were investigated. The TST and QFT-2G test were performed on all subjects.

RESULTS

In 109 subjects with a negative TST history, the TST results were converted to positive in 38 subjects. While the TST was positive in 48 subjects (25%), the QFT-2G test was positive in only five subjects (3%). The correlation of the QFT-2G with TST results was not significant. There was no relationship between contact score and the TST result. Twenty-nine subjects had TST positive responses (22%), but there were no QFT-2G positive responses in subjects with a mild contact score. Sixteen subjects had TST positive responses (31%), but two subjects showed positive QFT-2G results (4%) in the moderate contact score group. However, the positive response rate of the TST and QFT-2G test was the same percentage in the severe contact score group (33%).

CONCLUSION

The QFT-2G test showed a significant relationship with the contact score when compared with the TST. If the subjects with LTBI in the moderate contact score group were selectively excluded, the contact investigation in the mild contact score group may not be necessary. If there would have been many subjects with the QFT-2G positive responses in the moderate contact score group, we think that the QFT-2G test must be performed even in the mild contact score group.