Comparing interferon- gamma release assay with tuberculin skin test readings at 48-72 hours and 144-168 hours with use of 2 commercial reagents.
BACKGROUND
Despite widespread use, the tuberculin skin test (TST) has many limitations, including a requirement for a second visit between 48 and 72 hours. The goal of this study was to determine the reliability of a TST reading between 144 and 168 hours.


METHODS
Tuberculin antigen was applied into both forearms (Aplisol in one arm and Tubersol in the other, from single lots of each product) by the Mantoux method. Blood samples were obtained for interferon- gamma release assay. Subjects were seen at 48-72 hours for the initial (day 2) TST reading and returned at 144-168 hours for a second (day 7) reading.


RESULTS
A total of 116 subjects at increased risk for tuberculosis were studied; 25 (22%) had positive results at day 2 with Tubersol and 27 (23%) had positive results at day 2 with Aplisol. Overall agreement between Tubersol and Aplisol at day 2 was 93% (kappa = 0.80) and at day 7 was 94% (kappa = 0.76). Overall agreement between day 2 and day 7 was 89% for Tubersol and 86% for Aplisol. Discordant results between day 2 and day 7 occurred mostly in persons with a history of bacille Calmette-Guerin vaccination.


CONCLUSIONS
Subjects who fail to present at 48-72 hours for TST reading may still have a reliable TST reading at up to 168 hours. Aplisol and Tubersol reagents produce comparable results when compared with the interferon- gamma release assay.
Tat
David
D
Division of Infectious Diseases, Department of Internal Medicine, Wright State University School of Medicine, Dayton, OH 45409, USA.
Polenakovik
Hari
H
Herchline
Thomas
T
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007202:Indicators and Reagents; D007371:Interferon-gamma / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors; D014373:Tuberculin; D014374:Tuberculin Test / Q000379:methods*; D014376:Tuberculosis / Q000175:diagnosis*
D007202:Indicators and Reagents; D014373:Tuberculin; D007371:Interferon-gamma