She also pointed out that a significant amount of blood is required to perform an IGRA. “That might not always be optimal, especially in a young child,” Dr. Shane said. “Low CD4 counts and other immunodeficiencies have also been associated with false-negative TST and indeterminate/false-negative IGRA results.”
For contact investigations, IGRAs offer increased specificity, are completed during a single visit, and their response is not boosted if an additional evaluation is needed 8-10 weeks after exposure. For periodic screening of health care workers, IGRA offers “technical and logistical advantages, and two-step testing is not required,” she said.
If the TST or IGRA is positive, additional diagnostic efforts are needed “to differentiate between LTBI and active MTB,” said Dr. Shane, who recommended the Curry International Tuberculosis Center as a resource for clinicians. “Your clinical history, chest radiography, [and results of] sputum/gastric aspirates will help,” she added.
If the TST or IGRA is negative, “it’s not sufficient to exclude MTB infection. If you have a discordant TST and IGRA result, consider history and epidemiologic risk factors. Treat with clinical suspicion or risk of a poor outcome (those younger than age 5 and those infected with HIV).”
Dr. Shane reported having no relevant financial disclosures.
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