Table 2. Key Differences Between Tuberculin Skin Test (TST) and Interferon-γ Release Assay (IGRA) as Diagnostic Measures for Latent Tuberculosis Infection

Characteristics	TST	IGRA
Protocol^23,30	After 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 induration	After 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 sensitivity^21,32	75% to 90% (reduced in immunocompromised patients)	78% to 92%
Estimated specificity^21,32	70% to 95% (reduced in BCG-vaccinated and NTM infections)	93% to 98%
Advantages^23,33	No laboratory procedures or costs	May be more cost-effective
		Requires one visit
		Objectivity in test interpretation
Disadvantages³²	Requires follow-up visit (48 to 72 hours later)	Requires laboratory procedures
	High subjectivity in test interpretation	Should 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.