Performance of commercial blood tests for the diagnosis of latent tuberculosis infection in children and adolescents.

BACKGROUND

The accurate diagnosis of latent tuberculosis infection reduces the risk of progression to severe disseminated disease. However, in young children, a major limitation of the standard tuberculin skin test is that false-negative results cannot be detected. The new interferon-gamma release assays QuantiFERON-TB Gold (Cellestis Carnegie Victoria, Australia), QuantiFERON-TB In-Tube (Cellestis), and T-SPOT.TB (Oxford Immunotec, Abingdon, United Kingdom) show promise of greater accuracy, but they may also be affected by impaired cellular immunity, resulting in indeterminate results (ie, insufficient response in positive-control wells).

OBJECTIVE

To evaluate the impact of age on the performance of interferon-gamma release assays when used in a routine hospital setting among children tested for suspected active or latent TB infection.

METHODS

We retrospectively studied 496 children 0 to 19 years of age who had been tested with the tuberculin skin test and at least 1 interferon-gamma release assay: 181 with QuantiFERON-TB Gold and 315 with QuantiFERON-TB In-Tube. In 154 of the children, paired interferon-gamma release assay testing was available: 87 with QuantiFERON-TB Gold/T-SPOT.TB and 67 with QuantiFERON-TB In-Tube/T-SPOT.TB.

RESULTS

Compared with T-SPOT.TB, the rates of indeterminate results were significantly higher for both QuantiFERON-TB Gold and QuantiFERON-TB In-Tube. QuantiFERON-TB Gold and QuantiFERON-TB In-Tube also gave indeterminate results more frequently in children <4 years of age than in those >/=4 years of age. Indeterminate results were associated with younger age for both QuantiFERON-TB Gold and QuantiFERON-TB In-Tube but not for T-SPOT.TB. Considering age as a binary variable (<4 and >/=4 years of age), a significantly higher concentration of phytohaemagglutinin-produced interferon-gamma was observed in older children with both QuantiFERON-TB Gold and QuantiFERON-TB In-Tube.

CONCLUSIONS

Different blood tests for the diagnosis of latent tuberculosis infection in children seem to perform differently, because both QuantiFERON-TB tests were more likely than T-SPOT.TB to give indeterminate results in children <4 years of age.