A comparison of tuberculin skin tests and interferon-gamma release assays

  From Uptodate

A comparison of tuberculin skin tests and interferon-gamma release assays

	TST	IGRAs
Advantages	TST does not require equipment and can be done without a laboratory. It is less expensive than for IGRAs (but greater personnel time is required). Longitudinal studies have demonstrated the predictive value of TST, and randomized trials show that LTBI therapy is much more effective in those who are TST positive than TST negative.	IGRA does not require follow-up visit to complete the testing process (but follow-up visits may be needed for LTBI therapy). IGRA does not give false-positive results because of prior BCG vaccination.
Disadvantages	TST requires an intra-dermal injection and a subsequent follow-up visit with trained staff to interpret results in 48 to 72 hours. TST may give false-positive results because of prior BCG vaccination or sensitization to nontuberculous mycobacteria. TST may give false-negative results because of immunosuppression (eg, HIV or active TB), natural waning of immunity, and technical limitations (including reader variability). Serial TST interpretation is complicated by potential boosting, although this can be minimized through initial two-step testing. TST can cause adverse reactions (skin blistering and ulceration); these are rare.	IGRA requires a blood draw, laboratory equipment, and technical expertise for specimen collection, processing, and assay. Reagent costs are substantially higher than costs of TST. IGRA test results are available within 24 hours at the earliest. IGRA may give false-negative results because of immunosuppression (eg, HIV or active TB) and technical variability. Interpretation of serial IGRA is complicated by frequent conversions and spontaneous reversions and by lack of consensus on optimum thresholds for conversions.

TST: tuberculin skin test; IGRA: interferon-gamma release assay; HIV: human immunodeficiency virus; LTBI: latent tuberculosis infection; BCG: Bacillus Calmette-Guerin.

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