Rheumatology Advance Access originally published online on October 27, 2007
Rheumatology 2007 46(12):1863-1864; doi:10.1093/rheumatology/kem252
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Comment on: Use of the QuantiFERON TB Gold test as part of a screening programme in patients with RA under consideration for treatment with anti-TNF-
agents: the Newcastle (UK) experience
1Department of Rheumatology, Lincoln County Hospital, Lincoln LN2 5QY, 2Department of Respiratory Medicine, Glan Clwyd Hospital, Rhyl LL18 5UJ and 3Department of Rheumatology, Southport General Hospital, Southport PR8 6PN, UK
Correspondence to:V. Kaushik, Consultant Rheumatologist, Lincoln County Hospital, Greetwell Road, Lincoln, LN2 5QY, UK. E-mail: vvkaushik{at}hotmail.com
SIR, we read with interest the recent article by Pratt et al. [1] on the use of QuantiFERON-TB® Gold test (QTG) as a part of the screening programme in patients with RA under consideration for treatment with anti-tumour necrosis factor (TNF)-
agents. They conclude that the use of QTG test in this group of patients is feasible, useful, cost-effective and unaffected by the impaired immunocompetence of the group. However, before QTG testing can be advocated as a screening tool in these circumstances, we feel there are a number of unanswered questions.
In 2001, the QTG test was approved by the Food and Drug Administration as an aid for detecting latent Mycobacterium tuberculosis infection (LTBI) [2, 3]. Limitations of QTG include the need to draw blood and process it within 12 h after collection, and the limited laboratory and clinical experience with the assay. The utility of QTG in predicting the progression to active tuberculosis has not been evaluated. The Centre for Disease Control guidelines on the use of QTG does not recommend its use for the screening of children aged <17 yrs, pregnant women, or for persons with clinical conditions that increase the risk for progression of LTBI to active tuberculosis (TB) (e.g. human immunodeficiency virus infection, those receiving immunosupressing drugs, chronic renal disease, diabetes, etc.) [4]. It is currently recommended that the tuberculin skin test (TST) be employed in combination with a risk stratification strategy in these situations [5]. In other words, in the context of impaired immunocompetence, QTG faces the same limitations as TST. Since the cohort used in the study is identified as immunocompromised RA patients, this makes us wonder whether the negative QTG in 80% of the study population [1] were true negatives or those affected by poor T-cell response secondary to immunocompromise [6]. About 10% of LTBI cases will eventually progress to clinical TB infection, and therefore longer follow-up of the study cohort might provide useful data about the negative predictive value of this test.
Three out of the seven patients who had positive QTG did not receive treatment. This is not surprising and confirms earlier reports for the lack of the predictive value of positive blood test results for progression to TB [7]. Furthermore, many indeterminate test results seems to have compounded the picture rendering active decision making to no more than a qualified guess. The opportunity to compare the existing evaluation pathway with QTG analysis has not been provided by the authors, and it is therefore not possible to make an independent and informed observation about the added utility of QTG.
One of the potential advantages of QTG claimed over TST is that the studies have shown it being less affected by prior Bacille Calmette Guérin (BCG) vaccination [2]. However, a recent study on the risk factors for a positive TST clearly stated that having a BCG scar did not increase the risk of a positive skin test in unexposed individuals [8]. This again would question the cost-effectiveness in its use as a screening tool for TB exposure in low prevalence countries such as the UK.
We want to remind all readers that the TST is free of charge and all future tests should satisfy the health economic argument before being considered as an alternative screening tool, unless their superior specificity and predictive values would force a major shift in diagnostic and therapeutic pathways.
We believe that TST along with the risk stratification guidelines proposed by the British Thoracic Society [5] still remains an invaluable initial screening tool for LTBI in patients with RA. QTG test use, however, would probably be better restricted to a small group of patients with RA who have relatively short disease duration, who are on no or a small dose of steroids and are not at high risk of developing TB on ethnic or geographical grounds. Furthermore, studies to ascertain whether TST alone or in combination with the QTG test for screening of LTBI is cost-effective in reducing the disease burden of TB are awaited.
Disclosure statement: The authors have declared no conflicts of interest.
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- Pratt A, Nicholl K, Kay L. Use of the QuantiFERON TB Gold test as part of a screening programme in patients with RA under consideration for treatment with anti-TNF-alpha agents: the Newcastle (UK) experience. Rheumatology (2007) 46:1035–6.
[Free Full Text] - Pottumarthy S, Morris AJ, Harrison AC, Wells VC. Evaluation of the tuberculin gamma interferon assay: potential to replace the Mantoux skin test. J Clin Microbiol (1999) 37:3229–32.
[Abstract/Free Full Text] - Food and Drug Administration, Center for Devices and Radiological Health. QuantiFERON®-TB - P010033 [Letter]. MD: Rockville. Food and Drug Administration, 2002. Available at http://www.fda.gov/cdrh/pdf/P010033b.pdf.
- Centers for Disease Control and Prevention. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5202a2.htm.
- Ormerod LP, Milburn HJ, Gillespie J, Ledingham J, Rampton D. BTS recommendations for assessing risk and for managing Mycobacterium tuberculosis infection and disease in patients due to start anti-TNF-alpha treatment. Thorax (2005) 60:800–5.
[Abstract/Free Full Text] - Brock I, Ruhwald M, Lundgren B, Westh H, Mathiesen LR, Ravn P. Latent tuberculosis in HIV positive, diagnosed by the M. tuberculosis specific interferon-gamma test. Respir Res (2006) 7:56.[CrossRef][Medline]
- Lalvani A. Diagnosing tuberculosis infection in the 21st century: new tools to tackle an old enemy. Chest (2007) 131:1898–906.[CrossRef][Web of Science][Medline]
- Gustafson P, Lisse I, Gomes V, et al. Risk factors for positive tuberculin skin test in Guinea-Bissau. Epidemiology (2007) 18:340–7.[CrossRef][Web of Science][Medline]
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  A. Pratt, K. Nicholl, and L. Kay Comment on: Use of the QuantiFERON-TB(R) Gold test as part of a screening programme in patients with RA under consideration for treatment with anti-TNF-{alpha} agents: the Newcastle (UK) experience: reply Rheumatology, December 1, 2007; 46(12): 1864 - 1865. [Full Text] [PDF]
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