투베르쿨린 결핵 피부 반응 검사 시약을 근육에 주사했다면?
결핵 피부반응검사 시약 PPD는 피내주사가 원칙으로 정맥, 근육, 또는 피하주사를 하면 안된다. 그러나 간혹 바늘이 깊게 들어가 피하조직이나 근육에 시약을 주사하는 실수가 발생하기도 한다. 이런 경우 피부반응이 제대로 나타나지 않기 때문에 위음성으로 판정될 수 있다.
만약 실수로 PPD 시약을 근육주사로 주입했다면 어떻게 될까? NWT Tuberculosis Manual의 Section 4: TB Screening 부분을 보면 아래와 같은 설명이 나온다.
If the TST is accidentally given as a subcutaneous or an intramuscular injection, this should not pose a serious problem. It is possible that tuberculin-sensitive people would have localized inflammation, which should be self-limited.
다행히 건강에 위협이 되는 일은 없지만, 주사가 잘못 되었음을 인지하면 즉각 검사를 다시 시행해야 한다.
혹시 환자가 TST 재검사에 대한 신뢰를 가지지 못한다면 IGRA 검사를 고려할 수 있다. 이때 직전에 주사한 PPD가 IGRA 결과에 영향을 주지는 않는지 확인해보자. 퀴아젠의 퀀티페론(QuantiFERON®-TB Gold) FAQ를 훑어보면 다음과 같은 질의응답이 실려있다.
Does a prior TST influence a QFT result?
There is some conflicting evidence that suggests that a prior TST can induce a positive QFT result in an uninfected individual. One paper, based on the results from only 3 individuals, speculates that boosting does occur, but this has not been supported in much larger studies. Reports by Leyten et al and Richeldi et al clearly demonstrate that a TST placed 3 days prior to QFT, and up to 12 weeks later does not induce positive responses in those uninfected. The largest study on the effect of the TST on a QFT response was part of a CDC/US Military study in Navy recruits. Data from this study, reviewed by the US FDA and presented in the QFT Package Insert, found that in 530 subjects tested twice, 4 to 5 weeks apart, the reproducibility of QFT was 98.5%. Five recruits changed from positive to negative and 3 became QFT positive.
The above findings are in agreement with the general knowledge of how an immune response is generated. It would not be expected that uninfected individuals would mount a primary cellular immune response to the extremely small amounts of the TB-specific antigens used in QFT that are present in the aqueous tuberculin injected. However, it is possible that even very small amounts of ESAT-6, CFP-10 and TB7.7 (p4) may be present in tuberculin and could boost responses of individuals infected with M. tuberculosis, but not from BCG vaccination. There is evidence of this possibility in the studies published to date. To avoid a boosted response, QFT should be administered concurrently, or no later than 3 days after a TST(*).
In contrast to QFT, boosting is a common phenomenon when a TST is repeated. Injection of tuberculin for the TST can boost subsequent TST responses, due to remote TB infection, as well as infection with NTM or vaccination with BCG.
(*) RN van Zyl-Smit, R.N. et al. (2009) Within-Subject Variability and Boosting of T-Cell Interferon-γ Responses after Tuberculin Skin Testing. Am J Respir Crit Care Med 180, 49.
면역반응의 결과로 퀀티페론 양성이 나오는 경우도 있었지만 TST 주사 후 3일 이내에 퀀티페론 검사를 하면 부스터 반응으로 인한 위양성을 방지할 수 있다.