![]() ![]() Live-virus vaccines: Live-virus vaccines might affect IGRA test results. Similarly, COVID-19 vaccination should not be delayed because of testing for TB infection. These tests may now be administered without regard to timing of COVID-19 vaccination and can even be administered during the same encounter as COVID-19 vaccination. This recommendation reflected an abundance of caution during a period when these vaccines were new. The CDC previously recommended either the TST or IGRA be performed >4 weeks after completion of COVID-19 vaccination, to minimize potential interference between vaccination and TB testing. TB to evaluate only high-risk healthcare workers trended lower in reversion rate (mean 13.9%) when compared to hospitals evaluating all healthcare workers (mean 20.7%). In a study of over 16,000 healthcare workers across 19 US hospitals, the mean reversion rate was 17.6%. Reversion: the opposite of conversion-a result that goes from above the established cutoff to below the cutoff (positive to a negative). For patients and healthcare workers with weak-positive results in low-risk settings, CDC guidelines recommend retesting with an equivalent or other test while considering the full clinical picture and risk/exposure assessment. 4Ĭonversion rates correlate with geographic incidence of TB and/or known TB risk factors. 1,2,4 In a study of over 16,000 healthcare workers across 19 US hospitals, the mean conversion rate was 0.8% (range, 0.0%-2.5%). 1Ĭonversion: with respect to TB antigens, conversion is the point at which interferon gamma becomes detectable above the established threshold or cutoff from a previous negative or unknown result (negative to positive). Please refer to the package insert for full information on result reporting/interpretation. If the result is still Borderline (equivocal) on retesting with another specimen, then other diagnostic tests and/or epidemiologic information should be used to help determine the tuberculosis (TB) infection status of the patient. 1īorderline (equivocal): Results where the highest of the Panel A or Panel B spot count is 5, 6, or 7 spots are considered Borderline (equivocal) retesting by collecting another patient specimen is recommended. Negative: The test result is Negative if both (Panel A-Nil) and (Panel B-Nil) spot counts are ≤ 4, including values <0. Positive: The test result is Positive if (Panel A-Nil) and/or (Panel B-Nil) spot count is ≥ 8. TB test are interpreted by subtracting the spot count in the Nil control well from the spot count in each of the Panels, according to the following algorithm: 1 Test results are determined by enumerating the spots (captured interferon-gamma from individual T cells) in each of the patient’s 4 test wells (Positive Control, Nil Control, Panel A, Panel B). For all samples, the test controls, positive and negative, must perform as expected. ![]() TB test results are reported as positive, negative, or borderline (equivocal). If IGRAs are to be used in contact investigations, negative results obtained prior to 8 weeks after the end of exposure typically should be confirmed by repeat testing 8 to 10 weeks after the end of exposure.” ![]() IGRAs offer the possibility of detecting M tuberculosis infection with greater specificity than with a TST.
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