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Correspondence |

The Predictive Value of Interferon-γ Release Assays and Tuberculin Skin TestTB Tests and Unvaccinated Close Contacts: What About Those Not Vaccinated With Bacillus Calmette-Guérin? FREE TO VIEW

Eduardo Hernández-Garduño, MD; Gerardo G. Huitrón Bravo, MD
Author and Funding Information

From the Centro de Investigación en Ciencias Médicas, Universidad Autónoma del Estado de México.

Correspondence to: Eduardo Hernández-Garduño, MD, Centro de Investigación en Ciencias Médica, Jesús Carranza #200, Toluca, Estado de México, México, 50130; email: investigador.cicmed@gmail.com.


Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2013;143(5):1514-1515. doi:10.1378/chest.13-0055
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Published online
To the Editor,

In a recent meta-analysis in CHEST (July 2012), Diel et al1 concluded that interferon-γ release assays (IGRAs), including QuantiFERON-TB Gold (QFT-G) (Cellestis, a company of Qiagen GmBH), QuantiFERON-TB Gold In-Tube (QFT-GIT) (Cellestis, a company of Qiagen GmBH), and the T-SPOT.TB ELISPOT (Oxford Immunotec Ltd), have a higher positive predictive value (PPV) and negative predictive value (NPV) for progression to active TB compared with those of the tuberculin skin test (TST). The PPV and NPV in those not vaccinated with bacille Calmette-Guérin (BCG) was not shown because the majority of the study participants had a history of BCG vaccination. Therefore, the results should apply mostly to the BCG-vaccinated and not be generalized.

A previous study in contacts of patients with TB by the same authors2 disregarded the analysis in the population at the highest risk of disease, that is, BCG-unvaccinated close contacts exposed to patients who tested positive on smear with pulmonary disease. But further analysis found that the PPVs of QFT-GIT and TST were not statistically different.3 This indicates that both tests may predict TB disease similarly in this population. This is probably one of the reasons why the use of TST continues in most low-burden settings where the BCG vaccine has been discontinued.

The practice of latent TB infection (LTBI)-targeted screening using IGRAs is becoming more common, particularly for BCG-vaccinated immigrants living in low-burden settings where laboratory facilities are usually available and the government, medical plans, or research programs cover the cost of testing. However, if, in the real world of high-burden settings, the cost of screening with TST is high, then screening with IGRA is a luxury. Many IGRA research studies performed in high-burden settings frequently have to rely on the sponsor for total or partial funding, as was likely the case in many studies cited in this meta-analysis. Lowering the cost of IGRAs would encourage use by TB programs where they are more needed, identifying more BCG-vaccinated individuals with true infection and candidates for preventive treatment. In conclusion, further research is needed in BCG-unvaccinated close contacts of smear-positive patients to clearly establish similarities or differences in the PPV and NPV between IGRAs and TST, to determine whether there is any difference in the number of individuals identified for preventive treatment using each test, and to establish what the best cost-benefit is in this population.

References

Diel R, Loddenkemper R, Nienhaus A. Predictive value of interferon-γ release assays and tuberculin skin testing for progression from latent TB infection to disease state: a meta-analysis. Chest. 2012;142(1):63-75. [CrossRef] [PubMed]
 
Diel R, Loddenkemper R, Niemann S, Meywald-Walter K, Nienhaus A. Negative and positive predictive value of a whole-blood interferon-γ release assay for developing active tuberculosis: an update. Am J Respir Crit Care Med. 2011;183(1):88-95. [CrossRef] [PubMed]
 
Hernández-Garduño E. An update: the predictive value of QuantiFERON-TB-Gold In-Tube assay and the tuberculin skin test. Am J Respir Crit Care Med. 2011;183(3):414. [CrossRef] [PubMed]
 

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References

Diel R, Loddenkemper R, Nienhaus A. Predictive value of interferon-γ release assays and tuberculin skin testing for progression from latent TB infection to disease state: a meta-analysis. Chest. 2012;142(1):63-75. [CrossRef] [PubMed]
 
Diel R, Loddenkemper R, Niemann S, Meywald-Walter K, Nienhaus A. Negative and positive predictive value of a whole-blood interferon-γ release assay for developing active tuberculosis: an update. Am J Respir Crit Care Med. 2011;183(1):88-95. [CrossRef] [PubMed]
 
Hernández-Garduño E. An update: the predictive value of QuantiFERON-TB-Gold In-Tube assay and the tuberculin skin test. Am J Respir Crit Care Med. 2011;183(3):414. [CrossRef] [PubMed]
 
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