Table 3.
Test sensitivity and specificity depending on tuberculosis history and different approaches to the interpretation of semiquantitative trace-positive results for Mycobacterium tuberculosis detection by Xpert MTB/RIF Ultra (Xpert Ultra)
|
Sensitivity |
Specificity |
||||
|---|---|---|---|---|---|
| All culture-positive (95% CI; n/N) | Smear-negative, culture-positive (95% CI; n/N) | All culture-negative (95% CI; n/N) | No history of tuberculosis (95% CI; n/N) | Any history of tuberculosis (95% CI; n/N) | |
| Xpert | 83%(79–86; 383/462) | 46%(37–55; 63/137) | 98% (97–99; 960/977) | 98%(97–99; 715/727) | 98%(95–99; 244/249) |
| Xpert Ultra | 88%(85–91; 408/462) | 63%(54–71; 86/137) | 96% (94–97; 934/977) | 96%(95–98; 701/727) | 93%(89–96; 232/249) |
| Xpert Ultra, no trace* | 86%(82–89; 395/462) | 54%(45–63; 74/137) | 98% (96–98; 953/977) | 98%(96–99; 709/727) | 98%(95–99; 243/249) |
| Xpert Ultra, conditional trace† | 88%(85–91; 406/462) | 61%(53–70; 84/137) | 97% (95–98; 945/977) | 96%(95–98; 701/727) | 98%(95–99; 243/249) |
| Xpert Ultra, trace-repeat‡ | 87%(84–90; 404/462) | 61%(52–69; 83/137) | 97% (95–98; 944/977) | 97%(96–98; 707/727) | 95%(91–97; 236/249) |
Sensitivity varied little by history of tuberculosis and did not vary systematically. Data on tuberculosis history were not available for one patient.
Study participants testing tuberculosis-positive based on a trace-positive Xpert Ultra result (n=32) were reclassified as tuberculosis-negative.
Study participants testing tuberculosis-positive based on a trace-positive Xpert Ultra result were reclassified as tuberculosis-negative only if they had a history of tuberculosis (n=13).
Study participants testing tuberculosis-positive based on a trace-positive Xpert Ultra result had Xpert Ultra testing on a subsequent sputum specimen: if the subsequent sputum Xpert Ultra result was negative for M tuberculosis then the participant was reclassified as tuberculosis-negative; if the subsequent Xpert Ultra result was positive for M tuberculosis (any semiquantitative threshold), then the participant was not reclassified and remained tuberculosis-positive (14 out of 32 participants tested tuberculosis-negative on sample 2 and were reclassified; 14 tested tuberculosis-positive on sample 2 and were not reclassified; and four were were non-determinate by Xpert Ultra on sample 2 and were not reclassified).