クォンティフェロン®TB-3G検査の臨床的意義と評価

Notes of understanding QFT measurements

BCG接種者が多いわが国では，QFTが結核感染のスクリーニングには向いている．それゆえに接触者検診，医療従事者の結核管理，免疫抑制状態にある患者の結核感染スクリーニング，活動性結核の診断補助に有用である．しかし，その一方で結核感染後8週以上経過しないと検査上陽性化しない，測定したIFN-γ値が個体内で変動するなどの問題がある．また，活動性結核に対し特異度はほぼ100％に近いものの感度は決して100％ではないことも挙げられる．そのため，結核感染の診断時には，特にカットオフ値近傍であれば複数回の検査を行い，また臨床背景を加味し判断する必要がある．

Since QuantiFERON (QFT) is a suitable diagnostic measure in diagnose of TB infection in Japan where BCG vaccination is universal, QFT is useful for TB contact investigation, TB control of healthcare workers, screening for TB infection in immunocompromised patients and auxiliary diagnosis of active TB.　But it has to be taken into consideration that it requires approximately 8 weeks for conversion of QFT TB infection, and variability of the measurement of interferon-gamma (IFN-γ) within indivisuals.　In addition although specificity is as high as approximately 100%, sensitivity is not perfect even in cases of active tuberculosis.　Therefore it is important to carefully evaluate QFT results especially when the measurement of IFN-γ is around cut off level, for example, by performing multiple testing or considering clinical settings.