Comparison of GeneXpert accuracy in diagnosis of tuberculosis between patients with and without positive results of acid-fast bacilli smear and HIV.

BACKGROUND

There is controversy regarding the indications of conducting GeneXpert assay for patients suspected of tuberculosis (TB). Therefore, we compared the accuracy of the assay between patients with and without positive results of acid-fast bacilli (AFB) smear and HIV.

METHOD: The study was conducted on patients referred to Shiraz TB laboratory from March 21, 2022, to March 20, 2023. Considering culture as the gold standard, we determined and compared the accuracy of GeneXpert assay and area under the Receiver Operating Characteristic (ROC) curve between high- and low-risk groups, i.e., HIV-positive or AFB smear-positive ones vs. HIV-negative ones with negative AFB smear.

RESULT: There was not a significant difference between the accuracy of the high- and low-risk groups (91.34 vs. 92.44, p = 0.664). While the sensitivity (95.23), specificity (92.29), and NPV (99.72) in the low-risk group were high, the PPV of the group (39.89) was significantly lower (P < 0.001) than that of the high-risk group (83.86).

DISCUSSION: Because of the low PPV of the assay in HIV-negative patients with negative AFB smears, our study could not confirm the necessity of conducting the assay for the low-risk patients. However, the study indicated the necessity for patients with HIV or a positive AFB smear.