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Sensitivity and specificity of a gamma interferon blood test for tuberculosis infection
J A Streeton1, N Desem, S L Jones
1Mercy Private Hospital Consulting Suites, East Melbourne, VIC, Australia.
Insights
The gamma interferon (IFN-γ) blood test demonstrates high sensitivity and specificity for detecting tuberculosis infection. This IFN-γ assay offers a rapid and practical method for diagnosing Mycobacterium tuberculosis, particularly in immunocompetent individuals.
Area of Science:
- Immunology
- Infectious Diseases
- Diagnostic Medicine
Background:
- Tuberculosis (TB) remains a significant global health challenge.
- Accurate and timely diagnosis is crucial for effective TB management.
- Interferon-gamma (IFN-γ) release assays (IGRAs) offer an alternative to traditional TB testing methods.
Purpose of the Study:
- To evaluate the diagnostic accuracy of an IFN-γ blood test for tuberculosis infection.
- To determine the sensitivity and specificity of the QuantiFERON-TB assay compared to the tuberculin skin test (TST).
Main Methods:
- Analysis of heparinized blood samples from 952 volunteers using the QuantiFERON-TB assay.
- Measurement of IFN-γ levels in whole blood stimulated with purified protein derivative (PPD) or phytohaemagglutinin (PHA).
- Comparison of IFN-γ results with TST reactivity and clinical presentation.
Main Results:
- The IFN-γ assay showed a specificity of 98% and a sensitivity of 90% when compared to TST.
- The assay detected positive responses in 83% of individuals with active TB and 80% with inactive disease.
- The test demonstrated high agreement with TST in detecting TB infection.
Conclusions:
- IFN-γ measurement from PPD-stimulated lymphocytes is a specific, sensitive, and rapid method for detecting Mycobacterium tuberculosis infection.
- The IFN-γ assay is a potentially valuable tool for early TB diagnosis, especially in immunocompetent individuals.
- IGRAs like the QuantiFERON-TB test offer a practical approach to TB screening and diagnosis.
Setting:
Victoria, Australia.
Objective:
To determine the sensitivity and specificity of a gamma interferon (IFN-gamma) blood test for tuberculosis infection.
Design:
Heparinised blood samples from 952 volunteers were analysed using the QuantiFERON-TB blood test. The levels of IFN-gamma in whole blood aliquots stimulated in vitro with human, avian or bovine purified protein derivative (PPD), or phytohaemagglutinin (PHA), were compared to tuberculin reactivity and clinical presentation.
Results:
IFN-gamma (IU/ml) responses were expressed as % PPD/PHA response ratios. The proportion of responders detected by both the IFN-gamma assay and tuberculin skin test (TST) was not significantly different when the % human PPD response ratio was 15%. Using this threshold, the specificity of the IFN-gamma assay was 98% (407/417 individuals with no known exposure to tuberculosis were negative) and sensitivity was 90% (163/182 untreated TST reactors were positive). The test detected positive responses in 83% (10/12) of individuals with proven active disease, 59% (24/41) of those previously treated, 80% (134/168) of those with untreated inactive disease, and 43% (55/128) of those exposed but TST-negative.
Conclusion:
The measurement of IFN-gamma released from PPD-stimulated blood lymphocytes is a specific, sensitive and rapid method of detecting Mycobacterium tuberculosis infection. The IFN-gamma assay may be a useful and practical tool for the early diagnosis of tuberculosis infection, especially in immunocompetent individuals.