Association of Clinical Properties and Compatibility of the Quantiferon-TB Gold In-Tube Test with the Tuberculin Skin Test in Patients with Psoriasis

Abstract

BackgroundIndividuals with psoriasis show conflicting responses to the tuberculin skin test (TST), a commonly used screening test for latent tuberculosis infection. An alternative to TST is QuantiFERON-TB Gold In-Tube test (QFT-GIT), an in vitro interferon-gamma release assay. This study aimed to determine the effect of the clinical properties of psoriasis (disease severity and koebnerization status) on TST results and the agreement between the TST and QFT-GIT results in psoriatic patients.

MethodsOne hundred patients with mild to severe psoriasis were enrolled in this prospective cross-sectional study. Psoriasis properties, including disease severity (psoriasis area and severity index score and koebnerization status), latent tuberculosis infection risk factors, and bacillus Calmette-Guerin vaccination history, were recorded. All patients underwent a TST and QFT-GIT. TST positivity cut-off point was 10 mm for bacillus Calmette-Guerin-vaccinated patients and 5 mm for non-vaccinated patients.

ResultsPsoriasis area and severity index scores and koebnerization status did not correlate with TST diameters. Only one of the 23 koebnerization-positive patients developed koebnerization in response to TST. QFT-GIT positivity was prominently higher in the TST-positive group, and this was the only factor that differed between the TST-positive and TST-negative groups (P < 0.001).

ConclusionTuberculin skin test results were not affected by psoriasis severity or koebnerization status. QFT-GIT positivity was prominently higher in the TST-positive group (P < 0.001). Overall agreement between TST and QFT-GIT results was moderate ( = 0.413). Concurrent negativity (44%) was higher than concurrent positivity (27%).