An assessment of nucleic acid amplification testing for active mycobacterial infection

The sensitivity and specificity values shown in green represent median (range) values as meta-analysis could not be performed with that subgroup.

Incidence of TB based on WHO estimates from 2012: high incidence = > 100 cases per 100,000 people; medium incidence = 10–100 cases per 100,000 people; low incidence = ≤ 10 cases per 100,000 people

K = the number of studies; NAAT = nucleic acid amplification testing; TB = tuberculosis

The LR scattergram in Figure 13 shows that the summary LR+ and LR– values for all studies investigating the ability of AFB microscopy plus NAAT to correctly identify patients with TB compared with culture were mostly within the green bands or the upper of the two left quadrants. This suggests that negative AFB and NAAT results correctly identified most patients who were culture-negative, and a positive result for either AFB or NAAT was more likely than not to indicate a culture-positive result. The reduced confidence in correctly diagnosing patients with culture-positive TB when AFB and NAAT were used together was due to the higher false-positive rate for the combined tests when compared with culture; 12% for AFB plus NAAT compared with 2% for AFB alone (Appendix E) and 6% for NAAT alone (Figure 15). As discussed above, culture is an imperfect reference standard and it is likely that many of the patients with apparent false-positive results actually have TB.