An assessment of nucleic acid amplification testing for active mycobacterial infection

LR = likelihood ratio; NAAT = nucleic acid amplification testing

The SROC curve, which depicts the relative trade-off between true-positive and false-positive results, indicated that AFB microscopy performs well in predicting culture positivity, with an AUC of 0.94 (95%CI 0.92, 0.96). There was no threshold effect based on the AFB staining methodology, suggesting that it does not impact on the sensitivity or specificity of AFB microscopy when compared with culture (Figure 54). This lack of threshold effect suggests that the observed differences in sensitivity between studies using in-house NAATs (which favoured ZN staining) and commercial NAATs (which favoured fluorescent staining) were due to other differences that have not been identified. However, there was a threshold effect based on specimen type, with sensitivity being higher when sputum specimens were tested (Figure 54).

Figure 54 SROC curve for all studies investigating the sensitivity and specificity of AFB microscopy versus culture in the diagnosis of TB

AFB = acid-fast bacilli; AUC = area under curve; FL = fluorescent staining; SROC = summary receiver–operator characteristic; NAAT = nucleic acid amplification testing; ZN = Ziehl-Neelsen staining