QuantiFERON-TB Gold in-tube testing for tuberculosis in healthcare professionals

To assess the performance of the QuantiFERON-TB Gold in-tube (QFT-GIT) assay for tuberculosis (TB) screening using a convenience sample from among a population of healthcare provider (HCP) employees of a hospital.

For the individuals in our cohort, we reviewed occupational health records, including TB risk factors, and the results of QFT-GIT testing. We considered a QFT-GIT result of greater than 0.35 IU/mL to be positive; when we obtained a positive result from a specimen from a particular individual, we repeated testing on a fresh specimen from that individual.

Of the 758 HCP employees whose specimens we screened, 439 had negative QFT-GIT results with negative TB risk factors and 268 had a negative QFT-GIT result but had positive TB risk factors. QFT-GIT results were positive in 47 subjects. Of the positive participants, 12 had a mean TB antigen value (antigen minus nil stimulated concentrations [Ag-Nil]) of 0.61 on initial testing and had a negative result on repeat testing, 22 had a TB Ag-Nil of 1.19 on initial testing and had a positive result on repeat testing (P = .01).

The QFT-GIT assay is useful for screening HCPs. However, false-positive results occur, particularly in a borderline zone of less than 1 IU/ml. Re-evaluation by repeat testing of fresh specimens from the same individual should be considered in subjects whose specimens test within the low-level positive cutoff.