Comparison of the sensitivity and specificity of two whole blood interferon-gamma assays for M. tuberculosis infection

doi:10.1016/j.jinf.2008.02.011

Journal of Infection

Volume 56, Issue 5, May 2008, Pages 348-353

https://doi.org/10.1016/j.jinf.2008.02.011 Get rights and content

Summary

Objectives

To compare the sensitivity and the specificity of the QuantiFERON^®-TB Gold (QFT-G) and QuantiFERON^®-TB Gold In Tube (QFT-GIT) diagnostic tests for Mycobacterium tuberculosis infection.

Methods

One-hundred patients with culture and/or PCR confirmed M. tuberculosis infection and 168 volunteers with no risk factors for M. tuberculosis infection were tested to estimate sensitivity and specificity, respectively.

Results

Analysis of data from the tuberculosis (TB) patients with valid results found the sensitivity of QFT-GIT (92.6%, 87/94) to be significantly higher than that for the QFT-G test (81.4%, 79/97; p = 0.023). The specificity of both QFT-GIT and QFT-G was 98.8% (CI: 95.1%–99.8%) with 2 of the 160 low risk subjects with valid results for both tests being positive. Data analysis confirmed the manufacturer's recommended test cut-off as being optimal, but identified higher sensitivity could be obtained by using a lower cut-off, with only a moderate decrease in specificity.

Conclusions

The QFT-GIT test had enhanced sensitivity for detection of M. tuberculosis infection over the QFT-G test, whilst maintaining equivalent high specificity. The logistic benefits of the QFT-GIT test format, as well as its higher sensitivity, should enable enhanced TB control.

Introduction

Tuberculosis (TB) remains a major health problem in the world and it has been estimated that one third of the world's population is latently infected with Mycobacterium tuberculosis (Mtb), the causative agent of TB.¹ As one of the effective control measures for TB, many industrialized countries including Japan offer prophylaxis to individuals with latent tuberculosis infection (LTBI).2, 3 The tuberculin skin test (TST) has been the mainstay of LTBI diagnosis for nearly a century. However, the TST has a number of logistic and performance problems, perhaps the most critical being its poor specificity in many populations. Since most antigens in the purified protein derivative used for the TST are highly homologous to antigens of BCG and non-tuberculous mycobacteria (NTM), it is known that TST responses are confounded by prior BCG vaccination or NTM infection.⁴

Discovery of antigens encoded by the Regions of Difference (RDs) in the Mtb genome, but absent from the genome of BCG vaccine strains and most NTM, has enabled the development of more specific diagnostics for LTBI.⁵ We and others have demonstrated that one of these tests, QuantiFERON^®-TB Gold (QFT-G), detects both LTBI and active TB with high specificity.6, 7, 8, 9, 10, 11 QFT-G has now been approved as a diagnostic test for Mtb infection in several countries, including Japan. However it still has some limitations. A major logistic limitation is that blood has to be stimulated with the Mtb-specific antigens within 12 h of collection. Due to this limitation, use of QFT-G is restricted in places where laboratories or institutions are far away from the blood collection facility.

A new version of QFT-G, QFT-G In-Tube (QFT-GIT), has been developed in response to this limitation.¹² In QFT-GIT, blood is collected directly into a blood collection tube which contains the Mtb-specific antigens, ESAT-6 and CFP-10, as well as a peptide from the Mtb-specific antigen, TB7.7 (Rv2654). As the QFT-GIT method allows antigen stimulation of blood cells to occur without pipetting or blood handling, it allows testing at locations remote from a laboratory as long as a 37 °C incubator is available, as after incubation tubes can be transported to a laboratory (for the IFN-γ ELISA) within 3 days.

The sensitivity of QFT-GIT has been evaluated in a number of studies13, 14, 15, 16, 17, 18, 19 and although theory suggests it may be higher than that for QFT-G (because of immediate stimulation of lymphocytes with antigen after collection and the addition of three antigens in the one tube), a comparative study of sensitivity and specificity for Mtb infection has yet to be reported. In the present study, we compared the sensitivities and specificities of both QFT-GIT and QFT-G in patients with culture-proven Mtb infection and in subjects with no risk factors for Mtb exposure, respectively.

Section snippets

Participants

TB patients and healthy control subjects consenting to the study were enrolled after the protocol was approved by each institution's ethics committee. Subjects were enrolled into one of two groups; Group 1 consisted of student nurses (older than 17 years of age); and Group 2 consisted of patients clinically suspected to have active TB who had received less than 1 week of anti-TB treatment. For low-risk subjects enrolled into Group 1, subjects were asked to complete a questionnaire about possible

Study populations

A total of 101 subjects strongly suspected of active TB disease were recruited into the study and 100 of these had Mtb infection confirmed by bacteriological culture and/or positive nucleic acid amplification testing. Since one patient was diagnosed with M. avium infection, the result of this patient was omitted from total results. Results from the remaining 100 individuals, who had all received less than one week of anti-tuberculosis therapy at the time of testing, were used to estimate

Discussion

This study found the performance of the In Tube version of the QuantiFERON-TB Gold test to have the same specificity (98.8%) for Mtb infection as the QFT-G test and to be similarly unaffected by BCG vaccination. Using the manufacturer's recommended cut-off value of 0.35 IU/ml, observed sensitivity of the QFT-GIT test (92.6%) was significantly higher than that for the QFT-G test (81.4%). Agreement between the two tests was very high (99.4%) for the low TB risk group, but lower for the TB patients

Acknowledgements

We thank staff in nursing schools and hospitals for helping with blood and data collection. We also thank Ms. Ayako Watanabe, Yasuko Inoue, and Aya Sakai for technical support in ELISA assay. This study received support from The Research Project of Emerging and Re-emerging Infectious Diseases, Ministry of Health, Labor, and Welfare, Japan, and from Cellestis Ltd., Melbourne, Australia.

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ⁱ: Present address: Isehara Kyodo Hospital, 2-17-1, Sakuradai, Isehara City, Kanagawa 259-1132, Japan.

^j: Present address: Kawabe Internal Medicine Clinic, 2-1-3, Takeoka, Kiyose City, Tokyo 204-0023, Japan.

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Comparison of the sensitivity and specificity of two whole blood interferon-gamma assays for M. tuberculosis infection

Summary

Objectives

Methods

Results

Conclusions

Introduction

Section snippets

Participants

Study populations

Discussion

Acknowledgements

Lancet

Eur Respir J

Global tuberculosis control. Surveillance, planning, financing

Guidelines for the Investigation of Contacts of Persons with Infectious Tuberculosis

MMWR

TUBERCULOSIS. Clinical diagnosis and management of tuberculosis, and measures for its prevention and control. 2006

The tuberculin skin test

Clin Infect Dis

Specific detection of tuberculosis infection: an interferon-gamma-based assay using new antigens

Am J Respir Crit Care Med

Comparison of tuberculin skin test and new specific blood test in tuberculosis contacts

Am J Respir Crit Care Med

Discrepancy between the tuberculin skin test and the whole-blood interferon gamma assay for the diagnosis of latent tuberculosis infection in an intermediate tuberculosis-burden country

JAMA

Selected RD1 peptides for active tuberculosis diagnosis: comparison of a gamma interferon whole-blood enzyme-linked immunosorbent assay and an enzyme-linked immunospot assay

Clin Diagn Lab Immunol

Screening for tuberculosis infection using whole-blood interferon-gamma and Mantoux testing among Japanese healthcare workers

Infect Control Hosp Epidemiol

Clinical reevaluation of the QuantiFERON TB-2G test as a diagnostic method for differentiating active tuberculosis from nontuberculous mycobacteriosis

Clin Infect Dis

Risk for tuberculosis among children

Emerg Infect Dis