Table 2. Key Differences Between Tuberculin Skin Test (TST) and Interferon-γ Release Assay (IGRA) as Diagnostic Measures for Latent Tuberculosis Infection
Protocol23,30After the 0.1-mL intradermal injection of PPD of Mycobacterium antigens into the patient, the area is measured between 48 to 72 hours for size of indurationAfter taking a 3- to 5-mL sample of peripheral blood mononuclear cells from the patient, the response of IFN-γ production by T-lymphocytes upon stimulation with specific Mycobacterium tuberculosis antigens (CFP-10, ESAT-6, TB7.7) is measured within 24 hours
Estimated sensitivity21,3275% to 90% (reduced in immunocompromised patients)78% to 92%
Estimated specificity21,3270% to 95% (reduced in BCG-vaccinated and NTM infections)93% to 98%
Advantages23,33No laboratory procedures or costsMay be more cost-effective
Requires one visit
Objectivity in test interpretation
Disadvantages32Requires follow-up visit (48 to 72 hours later)Requires laboratory procedures
High subjectivity in test interpretationShould not be used in children <2 years of age because of limited data in children between 2 and 4 years of age
  • BCG, Bacillus Calmette-Guérin; IFN, interferon; NTM, nontuberculous mycobacteria; PPD, purified protein derivative.