Xpert MTB/RIF Results in Patients With Previous Tuberculosis: Can We Distinguish True From False Positive Results?

摘要: Background Patients with previous tuberculosis may have residual DNA in sputum that confounds nucleic acid amplification tests such as Xpert MTB/RIF. Little is known about the frequency of Xpert-positive, culture-negative ("false positive") results retreatment patients, whether these are distinguishable from true positives, and Xpert's automated filter-based wash step reduces false positivity by removing associated nonintact cells. Methods Pretreatment patients (n = 2889) symptoms Cape Town, South Africa, underwent a sputum-based liquid culture Xpert. We also compared dilutions intact or heat-lysed mechanically lysed bacilli. Results Retreatment cases were more likely to be false-positive (45/321 Xpert-positive false-positive) than new (40/461) (14% [95% confidence interval {CI}, 10%-18%] vs 8% CI, 6%-12%];P= .018). Fewer years since treatment completion (adjusted odds ratio [aOR], 0.85 .73-.99]), less mycobacterial (aOR, 1.14 1.03-1.27] per cycle threshold [CT]), chest radiograph not suggestive active 0.22 .06-.82]) positivity. CThad suboptimal accuracy for positivity: 46% Xpert-positives CT> 30 would positive, although 70% positives missed. CT's predictive ability (area under curve, 0.83 .76-.90]) was improved additional variables. detected nonviable, bacilli without change CTvs controls. Conclusions One 7 negative potentially positive. False recent tuberculosis, high CT, tuberculosis. Clinicians consider awaiting confirmatory testing 30; however, most fall below this cut-point. can detect