An assessment of nucleic acid amplification testing for active mycobacterial infection

AFB microscopy plus NAAT was most effective at confirming and excluding the presence of culture-positive disease in sputum specimens but could only confidently exclude culture-positive disease in non-sputum specimens (Figure 13B and C). When studies using either an in-house NAAT or the commercial NAAT in combination with AFB were analysed separately, the summary LR+ and LR– estimates for the AFB plus commercial NAAT were more effective at confirming the presence of culture-positive disease than AFB plus in-house NAAT for all specimen types. Furthermore, in non-sputum specimens a positive AFB or in-house NAAT result did not provide any useful information, most likely due to the 14% false-positive rate in this population. A negative AFB and commercial NAAT result was only able to confidently exclude the presence of culture-positive disease in non-sputum specimens.

The SROC curve shows no threshold effect when AFB microscopy is combined with either in-house NAAT or commercial NAAT (Figure 14). The SROC curves also show that when AFB microscopy plus NAAT was conducted in countries with a high incidence of TB, the results were less sensitive in sputum specimens and less specific in non-sputum specimens than when conducted in countries with an intermediate or low incidence of TB. The area under the curve (AUC) for AFB microscopy plus NAAT (0.97; 95%CI 0.95, 0.98) indicated that AFB plus NAAT performs well in predicting culture positivity (AUC > 0.9).