![]() 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. “An IGRA or a TST may be used without preference to test recent contacts of persons known or suspected to have active TB with special considerations for follow-up testing.“An IGRA is preferred for testing persons who have received Bacillus Calmette-Guérin (BCG) as a vaccine or for cancer therapy.”.“An interferon gamma release assay (IGRA) may be used in place of (but not in addition to) a tuberculin skin test (TST) in all situations in which CDC recommends TST as an aid in diagnosing adult M tuberculosis infections.”.Recommendations from the Centers for Disease Control and Prevention (CDC) state that 2,3 TB test is an indirect test for M tuberculosis infection (including disease) and is intended for use in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations. 1 It is intended for use as an aid in the diagnosis of M tuberculosis infection. TB test is an in vitro diagnostic test for the detection of effector T cells that respond to stimulation by Mycobacterium tuberculosis antigens ESAT-6 and CFP 10 by capturing interferon gamma (IFN- γ) in the vicinity of T cells in human whole blood collected in sodium citrate or sodium or lithium heparin.
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