Comparison of the QuantiFERON®-TB Gold assay and tuberculin skin test to detect latent tuberculosis infection among target groups in Trinidad & Tobago

Objective. To compare the QuantiFERON (R)-TB Gold (QFT-G) assay and tuberculin skin test (TST) in screening/diagnosis of latent tuberculosis infection (LTBI) among individuals in Trinidad & Tobago at high risk for TB. Methods. A total of 560 individuals (TB patient contacts, HIV patients, health care workers, prison inmates, and TB patients [controls]) were recruited for the study. Blood was drawn and processed using the QFT-G assay, followed by immediate administration of TST solution on subjects' forearm. Data were analyzed with Epi Info (TM) 3.5.1 software. Results were compared across the target groups using the chi-square test (P < 0.05). Results. The QFT-G assay detected LTBI in 51% of the subjects (with most positive results occurring among the control group) whereas the TST detected it in 39.4% (P = 0.001). Overall, the QFT-G assay detected LTBI more frequently than the TST among all subjects except the control group, where detection favored the TST. The QFT-G assay produced indeterminate and nonreactive results in some HIV patients but required less turnaround time than the TST (23.3 h versus 70.2 h; P < 0.0001). The TST cost less per subject than the QFT-G assay (US $3.70 versus US $18.60; P = 0.0008). Conclusions. The QFT-G assay cost more but had a higher detection rate among most target groups and required less turnaround time than the TST. However, its sensitivity was lower among immunocompromised subjects. Therefore, the QFT-G assay should be used with caution for LBTI screening/diagnosis in resource-poor, high-HIV prevalence settings such as Trinidad & Tobago.