HealthDay News — A change of QuantiFERON-TB interferon (IFN)γ values from <0.2 to >0.7 IU/mL is associated with an increased incidence in the rate of tuberculosis, according to a study published in the American Journal of Respiratory and Critical Care Medicine.

Elisa Nemes, PhD, from the University of Cape Town in South Africa, and colleagues assessed sources of QuantiFERON-TB variability and identified optimal procedures. The authors analyzed distributions of IFNγ response levels in healthy adolescents, Mycobacterium tuberculosis (M tb)-unexposed controls, and pulmonary tuberculosis patients.

The researchers found that IFNγ values were <0.2 IU/mL among individuals with no known M tb exposure.

 Tuberculin skin test positivity was 15%, 53%, 66%, and 91%, respectively, among individuals with IFNγ values <0.2, 0.2 to 0.34, 0.35 to 0.7, and >0.7 IU/mL. The incidence rates of tuberculosis were 10-fold higher for individuals who had a change in QuantiFERON-TB IFNγ values from <0.2 to >0.7 IU/mL, compared to those who maintained values <0.2 IU/mL over 2 years (P = .0003). Overall, 87% of patients with active TB had IFNγ values >0.7 IU/mL.

“Implementation of optimized procedures and a more rigorous QuantiFERON-TB conversion definition, an increase from IFNγ <0.2 to >0.7 IU/mL, would allow more definitive detection of recent M tb infection and potentially improve identification of those more likely to develop disease,” the authors write.

The study was partially funded by AERAS.

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Nemes E, Rozot V, geldenhuys H, et al. Optimization and interpretation of serial QuantiFERON testing to measure acquisition of M tuberculosis infection [published online July 24, 2017]. Am J Respir Crit Care Med. doi: 10.1164/rccm.201704-0817OC.