Chest Infections: Fellow Case Report Poster - Chest Infections II |

Quantiferon Testing Conundrums FREE TO VIEW

Leonel Carrasco, MD; Fareeha Hafeez, MD; Gene Pesola, PhD
Author and Funding Information

Harlem Hospital Center in Affiliation With Columbia University, New York, NY

Copyright 2016, American College of Chest Physicians. All Rights Reserved.

Chest. 2016;150(4_S):128A. doi:10.1016/j.chest.2016.08.137
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SESSION TITLE: Fellow Case Report Poster - Chest Infections II

SESSION TYPE: Affiliate Case Report Poster

PRESENTED ON: Tuesday, October 25, 2016 at 01:30 PM - 02:30 PM

INTRODUCTION: Quantiferon-TB Gold (QFT-G) testing is used to screen populations for latent Mycobacterium tuberculosis (MTB) since it requires only one patient visit (1). In low risk populations, false positive results can occur and can only be detected using a second screen (2). When the QFT-G results are unclear in immunocompetent subjects, PPD testing can help clarify MTB exposures.

CASE PRESENTATION: A 53 nonsmoking HIV negative female from Nigeria in the U.S. for 2 years had two QFT-G read as negative with both mitogen values greater than 9 IU/ml. Both TB - nil values were less than 0.10 IU/ml. However, a PPD placed 2 weeks after the second QFT-G test was 15 x 20 mm and was considered positive. Therefore, she agreed to and was treated for latent TB. This was considered a false negative QFT-G test. A 65 nonsmoking HIV negative male from the Dominican Republic had two QFT-G tests read as positive. Both tests had mitogen values greater than 6 IU/ml. However, the nil values were greater than 2 IU/ml in each test, albeit TB - nil values were both greater than 1.8 IU/ml. The tests were read as positive but due to the high nil values a PPD test was placed. The PPD reading was 0 x 0 mm. Therefore, this test was considered a false positive and the patient was not treated for latent TB. Both patients had no symptoms and both chest roentgenograms were normal.

DISCUSSION: When subjects are from areas of the world endemic for TB, negative QFT-G results should be challenged as possible false negatives. When QFT-G nil values are high, a PPD test should be considered since it will be more specific for the MTB antigen. High QFT-G nil values suggest other exogenous antigens have recently stimulated the patient’s lymphocytes making interpretation of TB exposure problematic.

CONCLUSIONS: QFT-G testing with interpretations are likely to be accurate when the mitogen level is high and the nil values (background) are low. When QFT-G testing does not meet clinical expectations in the immunocompetent patient, PPD testing can be a useful adjunct to further determine clinical status and appropriate treatment of the patient.

Reference #1: Mazarek GH, Jereb J, Vernon A, et al. MMWR 2010 59;RR05:1-25.

Reference #2: Pesola GR, Ahmad M, Badshah C. AJRCCM 2011;183:A4884.

DISCLOSURE: The following authors have nothing to disclose: Leonel Carrasco, Fareeha Hafeez, Gene Pesola

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