接觸TB後，TST大抵上2-12週轉陽，IGRA大抵上6-10週，但IGRA可以長到3個月以上 TB Tests Can Have a Lengthy Window Period Two studies suggest that interferon- release assay conversion sometimes occurs more than 3 months after exposure to active tuberculosis. Increasingly, interferon- release assays (IGRAs) are being used for diagnosing latent tuberculosis (TB). Although the tuberculin skin test (TST) traditionally used for this purpose converts to positive within 2 to 12 weeks after an individual is exposed to someone with active TB, the interval for IGRA conversion has remained unclear. Current guidelines recommend repeating an initially negative IGRA after 6 to 10 weeks, but this recommendation is not based on controlled studies. Two recent investigations address this issue. Anibarro and colleagues conducted a longitudinal prospective analysis among contacts of TB patients in Spain. The 152 contacts received a TST and an IGRA at first visit; for individuals with negative or conflicting results, t
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