Lakartidningen

TB can be detected with PCR - but only in smear-positive respiratory samples Unnecessary and inappropriate clinical requests represent a great waste of time and money and may also result in false diagnoses. PCR-techniques, such as Cobas TaqMan MTB, are used for rapid detection of tuberculosis (TB). These assays are only validated for respiratory specimens, but they are commonly requested also for non-respiratory specimens. These assays perform well in smear-positive respiratory samples, while the sensitivities are quite unsatisfactory for both respiratory and non-respiratory smear-negatives samples. The specificity is high and it is possible to rapidly distinguish between TB and infections caused by environmental mycobacteria. The analyses demonstrate, furthermore, that PCR assays cannot be used to evaluate treatment, detect relapses or exclude TB. Nor can these assays be used to evaluate contagiousness or to screen for TB.