Article Figures & Data
Figures
- Figure 1.
Procedure and result interpretation of ELISA T-cell–based gamma release essay. ESAT-6 and CFP-10 refer to specific antigens coded by the esat-6 and lhp genes of Mycobacterium tuberculosis. For indeterminate results, the test may be repeated if there is evidence of potential technical errors, such as storage at incorrect temperature, pipetting errors, etc.
Tables
QuantiFERON-TB Gold TST How is the test performed? Laboratory measurement of interferon-gamma in whole blood Intradermal injection of purified protein derivative and measurement of resulting induration What does the test measure? In vitro release of interferon gamma after exposure to specific M. tuberculosis antigens In vivo type intradermal hypersensitivity after injection of a mixture of mycobacterial antigens (not only M. tuberculosis) Ability to detect tuberculous infection Yes Yes Ability to distinguish latent and active tuberculosis No No False positive results Yes, but less frequently than with the TST. False-positive results may occur with exposure to selected nontubercular mycobacteria, but not after BCG vaccination. Yes. False-positive results may occur after exposure to nontubercular mycobacteria or after BCG vaccination. False negative results Possible among immunosuppressed individuals Possible among immunosuppressed individuals Effect of BCG vaccination None May give a false-positive result after BCG vaccination Need for patient to return for second visit No Yes, for reading of the skin reaction Required infrastructure Yes. Special equipment required in the laboratory No special infrastructure required. Easy to perform even in unsophisticated facilities Subjectivity in reporting results No Yes, it may vary depending on training of individual Cost More expensive Less expensive Time to obtain result At least 24 hours, but longer if run in batches At least 48 hours Boosting an anamnestic response with successive tests No Yes TST, tuberculin skin test; BCG, Bacillus Calmette-Guérin.
- Table 2.
Sensitivity and Specificity of QuantiFERON-TB Gold and Agreement Between QuantiFERON-TB Gold and Tuberculin Skin Testing
Agreement with TST 79–94 Specificity in latent tuberculosis 89–100 Sensitivity in latent tuberculosis 90 Specificity in active tuberculosis 97–100 Sensitivity in active tuberculosis 72–89 All values shown as percentages. TST, tuberculin skin test.
IGRA can be used in any evaluation for tuberculosis infection (active or latent). IGRA are more specific than TSTs, which may be positive because of previous BCG vaccination or exposure to non-tuberculosis Mycobacterium. A positive IGRA indicates tuberculosis infection but does not differentiate between active or latent infection. A negative IGRA excludes tuberculosis in immunocompetent patients. Immunosuppressed patients are more likely to have indeterminate results. IGRA does not require a second visit to read the results. IGRA is more costly and requires processing within 12 hours of collection. IGRA, interferon gamma release assays; TST, tuberculin skin test; BCG, Bacillus Calmette-Guérin.
Clinical Utility of Interferon Gamma Assay in the Diagnosis of Tuberculosis
